U.S. patent application number 11/440555 was filed with the patent office on 2007-11-29 for furnace for heating particles.
Invention is credited to Giang Biscan, Charles D. Blake, Ronald W. Cresswell, Robert E. Everhart, Hamid Hojaji, Thinh Pham, Mark G. Stevens.
Application Number | 20070275335 11/440555 |
Document ID | / |
Family ID | 38749940 |
Filed Date | 2007-11-29 |
United States Patent
Application |
20070275335 |
Kind Code |
A1 |
Biscan; Giang ; et
al. |
November 29, 2007 |
Furnace for heating particles
Abstract
A bottom-up cocurrent combustion furnace for the production of
synthetic microspheres by thermal expansion of glass particles is
provided having improved characteristics with regard to
anti-fouling, process efficiency, and yield. The disclosed furnace
uses preheated combustion air to preheat the feed material and to
convey the feed material in a dilute phase transport regime to a
burner. The combustion air, fuel, and feed material are premixed
prior to being injected though the burner. The feed material
rapidly expands as it is ejected through the burner and through a
flame and then rapidly cools to solidify the microspheres.
Additional features are provided to prevent the furnace from
fouling by keeping the feed material away from the furnace walls,
removing feed material that adheres to the furnace walls, and
collecting feed material that agglomerates or does not expand.
Inventors: |
Biscan; Giang; (Fontana,
CA) ; Blake; Charles D.; (Norco, CA) ;
Cresswell; Ronald W.; (North Sydney, AU) ; Everhart;
Robert E.; (Lake Arrowhead, CA) ; Hojaji; Hamid;
(Claremont, CA) ; Pham; Thinh; (Rancho Cucamonga,
CA) ; Stevens; Mark G.; (San Bernardino, CA) |
Correspondence
Address: |
GARDERE / JAMES HARDIE;GARDERE WYNNE SEWELL, LLP
1601 ELM STREET, SUITE 3000
DALLAS
TX
75201
US
|
Family ID: |
38749940 |
Appl. No.: |
11/440555 |
Filed: |
May 25, 2006 |
Current U.S.
Class: |
431/160 |
Current CPC
Class: |
C03B 19/102 20130101;
B22F 3/003 20130101; C03B 19/109 20130101 |
Class at
Publication: |
431/160 |
International
Class: |
F23D 11/36 20060101
F23D011/36 |
Claims
1. A furnace, comprising: a body, the body comprising one or more
walls defining a combustion chamber therein; a delivery system
having one or more conduits configured to convey fuel and feed
material to the body, and further configured to convey feed
material in a dilute phase transport regime such that the solids
content is less than about 1% by volume; a burner assembly
positioned within the combustion chamber, the burner assembly
having one or more injectors in communication with the delivery
system, the injectors configured to inject the fuel and feed
material into the combustion chamber; a cooling system in
communication with the one or more walls and configured to maintain
the walls below a pre-selected temperature; and an anti-fouling
system configured to keep feed material from adhering to the walls
and to remove feed material that contacts the walls, a portion of
the anti-fouling system comprising a vibrator configured to impart
a vibration to the body at variable frequencies to dislodge
particles adhered thereto.
2. The apparatus of claim 1, wherein the walls are constructed of a
non-refractory material.
3. The apparatus of claim 1, wherein the delivery system is
configured to mix the fuel and feed material prior to injection
into the combustion chamber.
4. The apparatus of claim 3, further comprising a combustion gas
delivery conduit in communication with the delivery system and
configured to mix fuel, feed material, and combustion gas prior to
injection into the combustion chamber.
5. The apparatus of claim 4, wherein the combustion gas has been
preheated.
6. The apparatus of claim 1, wherein the burner assembly further
comprises a diverging expansion cone extending away from the burner
such that the combustion gasses are allowed to expand to fill the
increasing volume provided within the expansion cone.
7. The apparatus of claim 1, further comprising a second wall
surrounding and generally concentric with, the body and spaced
therefrom such that an annular chamber is formed between the second
wall and the body, and wherein the cooling system comprises
circulated media delivered to the annular chamber to withdraw heat
from the body.
8. The apparatus of claim 7, wherein the circulated media is heated
within the annular chamber and is then diverted to the delivery
system and used as combustion gas.
9. The apparatus of claim 1, wherein the pre-selected temperature
is below the softening temperature of the feed material.
10. The apparatus of claim 1, further comprising a second vibrator
configured to cooperate with the first vibrator to apply one or
more selectable vibration modalities to the body.
11. The apparatus of claim 10, wherein one vibration modality is
mode 1 simple harmonic vibration.
12. The apparatus of claim 10, wherein the vibrators are configured
to operate out of phase with one another to apply a circular
vibration modality.
13. The apparatus of claim 1, further comprising a slag trap
configured to capture material at the bottom of the body.
14. The apparatus of claim 1, further comprising an additive
conduit configured to deliver an additive to the delivery system
such that the additive is mixed with the fuel and feed material
prior to injection into the combustion chamber.
15. The apparatus of claim 1, wherein the additive is provided to
coat the feed material to inhibit the feed material from adhering
to the body.
16. The apparatus of claim 1, further comprising expansion means
configured to allow the body to expand axially to accommodate
thermal expansion.
17. A furnace, comprising: a body comprising an inner cylinder
defining a combustion chamber therein, and a coaxial outer cylinder
spaced apart from the inner cylinder to define an annular chamber
therebetween; a delivery system in communication with the
combustion chamber comprising one or more conduits configured to
deliver feed material, fuel, air, and an anti-fouling additive to
the combustion chamber; and a burner assembly disposed within the
combustion chamber and in communication with the delivery system
and configured to inject the feed material, fuel, air; and the
anti-fouling additive into the combustion chamber, wherein the
anti-fouling additive is selected to inhibit the feed material from
adhering to the inner cylinder.
18. The furnace of claim 17, wherein the anti-fouling material is
significantly smaller than the feed material.
19. The furnace of claim 17, wherein the anti-fouling material is a
mixture of two or more materials.
20. The furnace of claim 17, wherein the anti-fouling material is a
mixture of kaolin and at least one other material.
Description
CROSS REFERENCE TO RELATED APPLICATION
[0001] This application claims the benefit of U.S. Provisional
Patent Application No. 60/648,480, filed May 25, 2005.
BACKGROUND OF THE INVENTION
[0002] The present invention relates generally to the processing of
particles and, more particularly, to a furnace for heating
particles.
[0003] Current furnaces for heating particles operate with a
sufficient amount of heat loss and are often energy inefficient.
Therefore, there remains a need to provide improved furnaces for
heating particles that reduce heat loss and are energy
efficient.
SUMMARY OF THE INVENTION
[0004] The present invention solves problems found with many
current furnaces for heating particles and are configured to reduce
heat loss and provide an energy efficient system. Furnaces of the
present invention also provide improved characteristics with regard
to anti-fouling, process efficiency, and yield.
[0005] The present invention includes a furnace configured to
process particles. The particles generally comprise one or more of
the following, such as powders, microspheres, solid particles,
hollow particles, solids, and/or other suitable precursors. Such
particles may include one or more precursors that are fed into the
furnace for heat treatment. Optionally or in addition, additives,
such as blowing agents, may be mixed with one or more precursors to
cause expansion of the precursor. Such additives may be mixed with
the precursor to achieve a desired output from the furnace.
[0006] Generally, a furnace of the present invention includes a
body comprising an inner cylinder defining a combustion chamber
therein, and a coaxial outer cylinder spaced apart from the inner
cylinder to define an annular chamber therebetween; a delivery
system in communication with the combustion chamber; and a burner
assembly disposed within the combustion chamber and in
communication with the delivery system The delivery system may
further comprise one or more conduits configured to deliver feed
material, fuel, air, and an anti-fouling additive to the combustion
chamber. The burner assembly may be further configured to inject
the feed material, fuel, air; and the anti-fouling additive into
the combustion chamber. The anti-fouling additive is typically
selected to inhibit the feed material from adhering to the inner
cylinder.
[0007] The present invention also includes a furnace having a body
with one or more walls defining a combustion chamber therein, a
delivery system having one or more conduits, a burner assembly
positioned within the combustion chamber, a cooling system in
communication with the one or more walls, and an anti-fouling
system configured to keep feed material from adhering to the walls.
The conduits may be configured to convey fuel and feed material to
the body, and further configured to convey feed material in a
dilute phase transport regime such that the solids content is less
than about 1% by volume. The burner assembly typically has one or
more injectors in communication with the delivery system, the
injectors further configured to inject the fuel and feed material
into the combustion chamber. The cooling system in typically
configured to maintain the walls below a pre-selected temperature.
The anti-fouling system is typically configured to also remove feed
material that contacts the walls. A portion of the anti-fouling
system may comprise a vibrator configured to impart a vibration to
the body at variable frequencies to dislodge particles adhered
thereto.
[0008] Those skilled in the art will further appreciate the
above-noted features and advantages of the invention together with
other important aspects thereof upon reading the detailed
description that follows in conjunction with the drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
[0009] For more complete understanding of the features and
advantages of the present invention, reference is now made to the
detailed description of the invention along with the accompanying
figures, wherein:
[0010] FIG. 1A depicts a schematic view of a vertical transport
furnace with cooled walls;
[0011] FIG. 1B depicts a schematic top view of the frame structure,
wherein a fabric material is attached to the frame structure;
[0012] FIG. 1C depicts a schematic view of a frame structure of
FIG. 1B for holding material and forming a wall of a furnace;
[0013] FIG. 2 depicts a schematic view of a vertical transport
furnace with an air buffer;
[0014] FIG. 3 depicts a schematic view of another embodiment of a
vertical transport furnace with an air buffer;
[0015] FIG. 4 is a schematic view of a non-vertical transport
furnace;
[0016] FIG. 5 is a schematic view of an inclined furnace;
[0017] FIG. 6 is a schematic view of a furnace employing radiant
energy;
[0018] FIG. 7 is a schematic view of a vortex type furnace;
[0019] FIG. 8 is a schematic view of a recirculating load type
furnace;
[0020] FIG. 9 is a schematic view of an annular recirculating load
type furnace;
[0021] FIG. 10A is a representation of a computer model simulation
displaying the effect of annular recirculating load type
furnace;
[0022] FIG. 10B is a graph representing swirl velocities at a first
cross section of the computer model simulation of FIG. 10;
[0023] FIG. 10C is a graph representing swirl velocities at a
second cross section of the computer model simulation of FIG.
10.
[0024] FIG. 11A displays temperature histories of particles in a
vertical transport furnace;
[0025] FIG. 11B displays histories of particles in an annular
recirculating load type furnace;
[0026] FIG. 12A is a schematic view of a burner system of a
furnace;
[0027] FIG. 12B is a schematic view of a modified burner system of
a furnace;
[0028] FIG. 13 illustrates a system having a spray dryer connected
to an annular recirculating load type furnace;
[0029] FIG. 14 illustrates a portion of the system of FIG. 13, the
illustration includes a representation of a computer model
simulation displaying the temperature distribution of the
particles;
[0030] FIGS. 15A and 15B are schematic views of a dryer-furnace
system;
[0031] FIG. 16 is a perspective view of a dryer-furnace system;
[0032] FIG. 17 is a cutaway view of the dryer-furnace system of
FIG. 16;
[0033] FIG. 18 is a circuit diagram for an air/gas control system;
and
[0034] FIG. 19 illustrates a vertical transport furnace having a
porous wall.
DETAILED DESCRIPTION OF THE INVENTION
[0035] Although making and using various embodiments of the present
invention are discussed in detail below, it should be appreciated
that the present invention provides many inventive concepts that
may be embodied in a wide variety of contexts. The specific aspects
and embodiments discussed herein are merely illustrative of ways to
make and use the invention, and do not limit the scope of the
invention.
[0036] In the description that follows like parts are marked
throughout the specification and drawing with the same reference
numerals, respectively. The drawing figures are not necessarily to
scale and certain features may be shown exaggerated in scale or in
a somewhat generalized or schematic form in the interest of clarity
and conciseness.
[0037] Various types of furnaces may be used to process particles.
The furnace design approaches may be applicable to various types of
furnaces. For example, some furnace embodiments are disclosed in
applicants co-pending application having Ser. No. 11/265057, filed
Nov. 1, 2005, entitled "A Furnace For Heating Powders and the
Like," the entirety of which is hereby expressly incorporated by
reference.
[0038] With reference to FIG. 1A, a vertical transport furnace 100
(VTF) with cooled walls includes a generally vertically oriented
elongated combustion chamber. The arrows in the FIG. 1A indicate
fluid flow. The elongated combustion chamber 105 has a disperse
mixture of processing gases (e.g., hot processing gases) and
particles 131 to be processed. An interior surface of the inner
cylinder 101 may define the combustion chamber 105. An outer
cylinder 102 may surround inner cylinder 101. A cooling chamber 116
is defined between the exterior surface of inner cylinder 101 and
the inner surface of outer cylinder 102. Cooling fluid 136 flows
through cooling chamber 116 and cools inner cylinder 101.
[0039] Particles 131 may include a precursor that is heat treated
within the furnace. During the heating process, such particles may
adhere to the interior surface of inner cylinder 101 and form
build-up. The wall temperature of inner cylinder 101 may be
maintained at or below a solidification temperature. When inner
cylinder 101 is at or below a solidification temperature, particles
contained in inner cylinder 101 may solidify before particles
contact inner cylinder 101. As particles approach the interior
surface of the inner cylinder, the particles are cooled and
solidify. These solidified or hard particles may be less likely to
adhere to the inner cylinder as compared to initial or
non-solidified (e.g., softer) particles.
[0040] Inner cylinder 101 may be adjusted or moved in order to
dislodge particle build-up. For example, the inner cylinder may be
vibrated to dislodge particles that are weakly adhered to the
interior surface of the inner cylinder.
[0041] The furnace may be designed to reduce the severity of
particle-wall impacts. Toroidal recirculation (spiral flow paths)
or swirl may cause the particles to impact the walls of the inner
cylinder without sufficient particle cooling. That is, the
particles may not be cooled enough to cause solidification as the
particles pass through a cool boundary layer along the interior
surface of the inner cylinder. Thus, soft particles may contact and
adhere to the inner cylinder. With the present invention, particles
may be directed along linear flow paths to reduce the number of
particles that impact the walls.
[0042] The cooling fluid may be recycled and used as combustion
air, thereby effectively returning the heat removed from the inner
cylinder back the combustion process. If the cooling fluid (e.g.,
cooling fluid that has passed through the cooling chamber and been
heated) is used as combustion air, thermal efficiency may be
increased. The furnace may require only as much air to be heated as
is required for complete combustion and the liberation of enough
heat to bring the particles to a desired process temperature. The
heat loss through the walls scales with the radius of the inner
cylinder. However, the drop in bulk temperature along the axis due
to that heat loss scales with the inverse of the square of the
radius. Hence, heat loss per unit volume generally varies as the
inverse of the furnace radius.
[0043] The maintenance of the temperature of the interior wall of
the inner cylinder below the processing temperature causes a drop
in average bulk temperature along the particles' flow path due to
radiation losses. In addition, avoidance of toroidal recirculation
may reduce the efficacy of mixing the hot gases and the solid
particles within the inner cylinder, and may lead to a less than
optimum radial temperature profile. Thus, particles may have
different processing histories depending on their radial location
within the inner cylinder during the heating process.
[0044] With respect to FIG. 1B, inner wall 101 may comprise a
material that inhibits or prevents particle build-up. In some
embodiments, the inner wall or column may comprise a fabric
material 112. Fabric material 112 may be a high temperature fabric
that is attached to a frame 111. Preferably fabric 112 may
withstand typical processing temperatures of the combustion
process. A high temperature fabric may be attached to frame 111 by
stitching, fasteners, adhesives, and/or any other suitable
attachment means for securing fabric 112 to frame 111.
[0045] Frame 111 may comprise one or more elongated frame supports.
The illustrated frame 111 of FIGS. 1B and 1C has a plurality of
elongated frame supports that are spaced from each other and form a
cylindrical inner wall 101. The high temperature fabric 112 may be
stretched over frame 111. Thus, high temperature fabric 112 may be
tensioned and supported by the elongated frame supports. One or
more expanders may be used to tension the fabric. The illustrated
expanders 126 of FIG. 1C are in the form of a concertina expander;
however, other types of expanders may be employed.
[0046] In some embodiments, fabric 112 may be slightly porous to
permit migration of fluid through the fabric 112. Fabric 112 may
permit the egress and/or ingress of fluid therethrough. The
illustrated fabric 112 permits ingress of cooling air 107 from
cooling chamber 116 into combustion chamber 105. Cooling air 107
passing through fabric 112 may dislodge particle build-up and/or
may form a protective barrier layer that reduces particle
impact.
[0047] Additionally, fabric 112 may be adjusted, e.g., vibrated, to
reduce or prevent particle build-up. Turbulence in the cooling
channels may cause continuous vibration of inner cylinder 101, thus
eliminating the need for mechanical vibrators. This may improve
fatigue levels and also reduce noise pollution while reducing or
eliminating particle build-up. In some embodiments, high
temperature fabric 112 may be releasably coupled to frame 101 so
that fabric 112 may be quickly replaced, removed and cleaned,
and/or the like.
[0048] Vertical transport gas buffer (VTGB) furnaces may have a
system for reducing or substantially eliminating particles
impacting the wall of the inner cylinder. The particles may be
transported in a vertical direction, either with or against gravity
as is the case of the VTF described above. To reduce or
substantially eliminate particles from contacting a wall of the
furnace, the walls are spaced from the particles passing through
the furnace. The illustrated furnace 200 of FIG. 2 has a combustion
chamber 205 that has a cross section that is gradually enlarged
along the flow path of the particles. The sidewalls of the furnace
may be distanced from each other such that particles do not contact
the sidewalls.
[0049] Referring now to FIG. 2, a flow comprising buffer gas 237
(e.g., hot air/flue gas) may form a protective barrier layer that
inhibits particles from contacting the wall of the furnace. The
illustrated furnace 200 has a gas stream 237 along the wall to form
a boundary layer to maintain a particle-free boundary layer
adjacent to the walls. One or more injection ports 214 may be
positioned at some point along the interior surface of furnace 200
to inject a buffer gas 237 into combustion chamber 205. Buffer gas
237 may be preheated fluid (e.g., air), non-preheated fluid,
combustible gas mixture, and/or other suitable fluids for forming a
buffer layer.
[0050] With respect to FIG. 3, a furnace may comprise a louvered
wall configured to allow fluid(s) to form a boundary layer. The
illustrated furnace 300 comprises a stack of metal (e.g.,
Inconel.RTM. alloy) rings 301 that form a louvered wall that allows
gas (e.g., cooling gas) to form a thin boundary layer along the
interior surface of the wall.
[0051] With respect to FIGS. 2 and 3, when particle-wall impact is
of little effect (or when significantly avoided), the walls may be
run at relatively higher temperatures, thereby reducing the
radiative heat losses. Walls may be constructed from ceramics or
other refractory material. In addition, if the walls are cooled by
introduced buffer air, then radiative heat losses may be quickly
returned to the furnace without the need to recycle the air as
combustion air.
[0052] The introduced buffer gas 237 is preferably heated to the
furnace temperature to maintain the particles at a desired
temperature. Additional energy may be required to heat the buffer
gas to the desired temperature. Also, the volume of additional air
to form buffer layers may be approximately twice the amount of air
used for wall cooling, as shown in FIG. 1.
[0053] With reference to FIG. 4, air 435 may be introduced through
the walls of a furnace 400 to provide a buffer and prevent
particle-wall impacts. The buffer layer may increase the mass flow
rate through furnace 400. The illustrated furnace 400 has buffer
gases that form a buffer that facilitates the flow of precursor 431
from the upper end of the furnace 403 to the lower end 404 and
final removal of product. This increase in mass flow in a furnace
may require increasing the axial flow speed and/or the cross
sectional area of the furnace. The shape and size of combustion
chamber 405 may be varied to achieve a desired flow rate of the
particles. The cross section of combustion chamber 405 may be
circular, polygonal (including rounded polygonal), and the like.
The cross sectional area of combustion chamber 405 may be increased
along the length of the combustion chamber. For example, combustion
chamber 405 may have a generally annular conical geometry as shown
in FIG. 4.
[0054] With reference again to FIG. 4, buffer gas 435 may be
introduced through the inner wall 401 and/or outer wall 402.
Precursor material 431 is introduced into furnace 400 through top
annulus opening 414. Transport air, preferably a minimal amount,
and/or hot flue gases may be combined with precursor 431 and
delivered through opening 414. The flue gas may be produced by a
commercial or in-house burner.
[0055] Optionally, precursor material 431 may be introduced with a
swirl component to increase transport velocity in order to aid
fluidization of the particles. The centrifugal forces associated
with this swirl component may reduce the number particles that
contact inner wall 401 by modifying the particles' drift trajectory
to an outwardly directed spiral, in contrast to the vertical drift
trajectory of particles illustrated in FIG. 1.
[0056] Buffer gas 435 may be directed through the walls of furnace
400 to reduce turbulence. Optionally, buffer gases 435 introduced
through the walls of furnace 400 may also contain a swirl component
to maintain the bulk flow swirl, thereby limiting the natural
erosion by energy losses in the bulk flow due to turbulence.
[0057] In some embodiments, by maintaining the sectional width of
furnace 400 as the cross sectional area increases, self-similarity
in the flow pattern between the wall flow and the transport flow
may be maintained throughout a substantial portion or the entire
furnace 400. Thus, wall jets may produce particle-free walls and
may maintain the swirling action of the main flow in combustion
chamber 405.
[0058] The feed rate of solids 431 and buffer gas flow 435 may be
selected to achieve the desired bulk flow rate. Furnace 400 may
have a control unit to selectively control the flow of buffer gas
435 and the feed rate of solids 431 in order to limit or prevent
fluctuations in the bulk flow rate, which may cause particle-wall
impacts resulting in stoppages for maintenance.
[0059] A non-vertical transport furnace may comprise a louvered
wall. The louvered allows cooling gas to form a thin boundary layer
on the inside of the wall. The particles are delivered into an
opening at the top of the furnace. The particles may flow through
the combustion chamber and are heated therein.
[0060] Inclined furnaces may use the buffer gas to aid in the
transport of solids through the furnace. The buffer gas may be
employed to reduce the amount of transport air mixed with
particles. As shown in FIG. 5, a combustion chamber 505 is
positioned between a plurality of upper radiant heaters 508 and a
plurality of outlets or injection ports 514. In some embodiments,
solids 531 are fed into the furnace 500 and buffer gas 535 carries
the solids through at least a portion of combustion chamber 505. A
plurality of buffer gas outlets 514 is defined in a lower floor 504
and may be positioned along the length of combustion chamber 505.
Lower floor 504 may be made from perforated or porous material.
[0061] Buffer gases 535 are continuously passed through lower floor
514 and into combustion chamber 505. In operation, buffer gases 535
may travel down the delivery line and pass through outlets 514
positioned along the length of the combustion chamber 505 and into
combustion chamber 505. Buffer gases 535 form a boundary layer that
protects lower surface 504 of combustion chamber 505 and promotes
the downhill transport of solids.
[0062] The inclined furnace of FIG. 5 employs reduced amounts of
transport air resulting in a more energetically efficient furnace.
Buffer gases 535 may maintain the temperature of lower floor 504
temperature at acceptable limits. The mass flux may be increased
down length of furnace 500 to progressively fluidize the particles
until particles 532 are delivered out of the exit 524 in a
partially or fully fluidized state. Heating the solids with radiant
heaters may be relatively expensive. Natural gas fired heaters may
be used to reduce production costs. The concentration may require
large footprint of the furnace in order to process large quantities
of material.
[0063] With reference to FIG. 6, a heating system has a radiant
heat source comprising one or more energy sources adapted to emit
electromagnetic energy. The illustrated furnace 600 has an energy
source in the form of a high power laser 620 (e.g., a CO.sub.2
laser). Laser 620 is directed to emit energy that heats the
particles 631 passing through a cavity 605 in the furnace. The
emitted energy 618 passes through the large cavity walls and is
reflected by one or more mirrors 619 defining the cavity.
[0064] The illustrated heating system comprises an upper opening
614 positioned above the cavity. Solids 631 are fed through opening
614 and fall through a processing section of cavity 605. In the
illustrated embodiment, the processing section of cavity 605 is
bounded by opposing pairs of reflective surfaces 619 (e.g.,
mirrors), which are preferably slightly non-parallel such that
successive reflections of beam 618 sweep out a path in 3D space
occupying a substantial portion or the full volume of the
processing section. The beams of light 618 heat the particles as
particles 631 pass through the processing section. Alternatively,
the heating system may have a plurality of energy sources that are
used with or without reflective surfaces. Additionally, the
reflective surfaces 619 may have a plurality of surfaces that are
angled to each other to reflect beams 618 in a variety of
directions.
[0065] The emitted beam 618 wavelengths may be selected such that
the precursor material 631 preferentially absorbs the incident
radiation and the transport air does not absorb energy. After
falling through processing section 605, particles 631 are
significantly hotter than the carrier gas. The carrier gas
functions as a quench gas by absorbing the heat from the particles.
The carrier gas preferably cools the particles sufficiently to
cause solidification of the particles before product removal 632 at
the base of the system.
[0066] The heating system 620 of FIG. 6 may result in an energy
saving of about 50% of the energy in a VTF, wherein the transport
air must be heated. If the energy source is a laser, the cost of
heating the particles may be relatively high because lasers are
power by electricity, which costs 15 times as much per unit energy
as natural gas. Hence, a heated system with an energy source in the
form of a laser may be 7.5 times more expensive than VTF systems
using natural gas.
[0067] FIG. 7 illustrates a vortex type furnace 700 having a
combustion chamber 705 defined by a cylindrical outer wall 702. An
injection system feeds precursor 731 into the combustion chamber
705. The combustion chamber 705 is configured such that combustion
process occurs in a central swirling region 709 into which the
precursor material is injected. The precursor 731 is heat treated
in this region as the particles travel along a somewhat spiral flow
path. Cool quench air 736 is injected at the outer regions of the
furnace 700 so as to form a cool outer barrier layer through which
particles 731 must pass before leaving the vessel and/or impacting
the sidewalls. The quench air 736 may promote the whirling or
circular motion of the particles. The illustrated quench flows 736
are directed along the sidewalls of furnace 700.
[0068] The maintenance of a cool zone defined by the flow of quench
air at the periphery of combustion chamber 705 results in a high
temperature differential between combustion zone 705 and
surrounding environment. The swirling motion of the solids and
combustion gases promotes mixing. The combustion process is
continually compensating due to the cool air being mixed into the
central combustion zone.
[0069] FIG. 8 illustrates a recirculating load furnace 800. A
recirculating load or RL Type furnace 800 separates the flow speed
for maintain good fluidization of the particles 831 and the
transport speed through the furnace by introducing a high degree of
swirl in the plane generally orthogonal to the to the axial
direction of transport through the furnace. This flow pattern
results in substantially the same volumetric throughput of gas as
in a VTF, but with a significantly reduced transport velocity
allowing for an increased cross sectional area of the furnace.
Additionally, the walls may be outwardly spaced from the particles
being processed in the combustion chamber 805 to reduce wall
impacts.
[0070] As shown in FIG. 8, hot combustion gases 823 from a separate
burner are introduced tangentially at the top of the furnace. The
precursor material is introduced at a central portion of combustion
chamber 805. The illustrated precursor material 831 is introduced
close to, but not at, the centerline of the combustion chamber. The
precursor material 831 picks up some swirl component as the
material drops and begins to flow along a spiral path towards
discharge ports 832.
[0071] Before the radius of the spiral flow paths reach the radius
of the combustion chamber (where wall impacts would occur), quench
air 836 is introduced tangentially, rotating either in the same
direction or in the opposite direction as the precursor flow
(depending on whether swirl is desired in the exit line). The swirl
component provides the main contribution to the fluidization speed,
thereby maintaining a good dispersion of particles. The vertical
component of the flow determines the volumetric usage of air and
gas.
[0072] By limiting or eliminating wall impacts, furnace 800 may be
refractory lined and thermally insulated. A highly efficient
heating process may be achieved because the furnace may use reduced
amounts of air and fuel which are used to bring precursors 831 to a
desired process temperature.
[0073] The air tangentially at the outer edge of furnace 800
promotes a flow pattern that may resemble solid body rotation. As
particles 831 pick up a swirl component, the radius of the
particles flow path may be increased due to centrifugal forces.
[0074] The RLF may have a flow field with a maximum swirl velocity
towards the outside wall of the combustion chamber. An annular
recirculating load furnace (ARLF) 900 of FIG. 9 may have a circular
flow that is driven from the inner surface 901 and/or outer surface
902 defining a combustion chamber 905.
[0075] The velocity field of the ARLF may have a maximum swirl
component proximate inner wall 901. The velocity field's swirl
component is reduced towards outer wall 902 of furnace 900. Thus, a
large initial centrifugal force is imparted on particles 931 which
begin a trajectory taking particles 931 away from inner wall 901.
As particles 931 approach outer wall 902, the centrifugal force
diminishes and reduces the likelihood that particles 931 impact
outer wall 902.
[0076] With continued reference to FIG. 9, inner wall 901 is
generally a cylindrical wall that extends axially along the furnace
900. A delivery system is positioned proximate an annular opening
914 at one end of furnace 900. The annular opening 914 is
configured to permit feeding of solids 931 into combustion chamber
905. A hot gas delivery system further comprises a plurality of
delivery ports 937 positioned along the inner wall. The ports 937
of the delivery system may be space about inner wall 901 and are
positioned below annular opening 914. Ports 937 may direct gases
from burners into the combustion chamber 905 such that the gases
and solids circulate through combustion chamber 905. Preferably the
combustion gases swirl about inner wall 901.
[0077] The particles 931 may be introduced through annulus opening
914 at the top of furnace 900. The diameter of annulus opening 914
may be relatively large to prevent excessive particle
concentrations, as compared to the central injection system of the
vortex type furnace. Initial particle motion is vertically downward
so that the particles 931 form a curtain surrounding injection
ports 937 for delivering combustion gases into the combustion
chamber 905.
[0078] The combustion gases may be injected with a radial and/or
tangential component. Preferably, combustion gases are injected at
a velocity with a minimal vertical component. In some embodiments,
the combustion gases are injected at a velocity with no vertical
component to increase the velocity differential between the
particles and combustion gases, thereby producing optimized heat
transfer rates in the initial mix section. This results in rapid
heating of the particles to a desired process temperature.
[0079] The quench air system is positioned between delivery system
and an end of combustion chamber 905. The quench air system may
comprise one or more quench ports 915 and 916 positioned to direct
quench air 936 into the combustion chamber 905. The ports 915 and
916 of the quench air system are defined by inner wall 901 and/or
outer wall 902. In some embodiments, including the illustrated
embodiment of FIG. 9, the quench air system has an inner quench
system having inner ports 915 positioned along inner wall 901 of
the furnace and an outer quench system having outer ports 916
positioned along the outer wall 902 of the furnace 900. The outer
quench system and the inner quench system direct air to promote
annular flow through the combustion chamber 905.
[0080] In some embodiments, quench air 936 may be introduced along
the floor of the chamber through a plurality of jets. For example,
a series of floor jets may inject and direct gases that sweep the
product radially outwards to a collection chamber. The collection
chamber may be positioned exterior to the outer wall of the furnace
or at any suitable position for receiving product.
[0081] Dispersed particles are introduced through the opening into
the combustion chamber and form a curtain of particles. Hot
combustion gases delivered by the delivery system and may pass
through a curtain of particles before forming the furnace flow and
may result in rapid equalization of gas and particle temperatures.
The equalization process leads to more uniform temperature
distributions in the furnace. The temperature of the gas and
particles may be maintained at a desired mixed temperature.
[0082] With continued reference to FIG. 9, particles 931 may flow
within the combustion chamber 905 without contacting inner wall 901
and/or outer wall 902. The outwardly directed centrifugal force on
particles 931 may limit or substantially eliminate the amount of
particles that contact inner wall 901. The larger particles in the
solids fed into combustion chamber 905 may move towards outer wall
902 faster than smaller particles. The centrifugal force depends on
the mass of the particles, the speed of rotation of the particles,
and the distance from the center or rotation to the particles. The
particles may experience centrifugal force as the particles move
away from the inner wall towards the outer wall. Quench air 936 may
flow from the outer quench system and form a protective barrier
layer that prevents particles from contacting outer wall 902.
[0083] Optionally, various drying systems or output systems may be
used with the ARLF. For example, a spray dryer, cyclone output, and
the like may be mounted directly to the furnace.
[0084] The annular combustion chamber 905 is defined by inner wall
901 and outer wall 902. The combustion chamber has an inner
diameter of about 1 meter (m), 2 m, 2.5 m, 3 m, 3.5 m, and ranges
encompassing such diameters. The outer diameter of combustion
chamber 905 is about 1.5 m, 2.5 m, 3 m, 3.5 m, 4 m, 4.5 m, 5 m, and
ranges encompassing such diameters. The width of combustion chamber
905 may be greater than about 1 m, 1.5 m, 2 m, and 2.5 m. The width
of combustion chamber 905 may be substantially constant or may vary
in the longitudinal direction. The distance from opening 914 and
the region where the particles are introduction to quench gas is
about 2 m. In some embodiments, furnace 900 has about 4 inches of
refractory lining, which equals about 13 tons.
[0085] FIG. 10A depicts a combustion chamber 905 having an inner
diameter of about 2.5 m, outer diameter of about 4 m, and a height
of about 2 m. Particles may have diameters in the ranged of about
100 .mu.m-200 .mu.m, and the furnace uses similar quantities of air
and natural gas as the furnace of FIG. 1. The solid loading rate is
equivalent to 3.6 tons/hr.
[0086] Velocities taking two different cross sections of the
furnace show the distribution of azimuthal (swirl) velocity. FIGS.
10B and 10C show the velocity of the particles. FIG. 10B shows the
azimuthal velocity of the particles at a first cross section of the
combustion chamber. FIG. 10C shows the azimuthal velocity of the
particles at a second cross section of the combustion chamber
positioned below the first cross section. There are relatively high
particle velocities of the particles are proximate to the top of
the furnace. The peak velocities are close to inside wall 901. Flue
gases (at about 1700.degree. C.) are directed generally
horizontally into the combustion chamber as the particles flow in a
generally vertical direction. The flow of particles form an annular
curtain of dispersed particles extending from the opening.
[0087] The somewhat large difference between the velocity of the
flue gases and the velocity of the particles may promote a high
initial rate of heat and momentum transfer to promote mixing of the
gases and particles. The flue gases and particles may quickly reach
a desired mixed temperature. The particles pick up a swirl
component and the maximum swirl velocity follows the maximum in
particle concentration as the particles pass down the combustion
chamber.
[0088] FIGS. 11A and 11B show a comparison between the
time-temperature histories of particles in the ARLF (FIG. 11B) with
those from a detailed simulation of a VTF (FIG. 11A). The large
variation in the time-temperature histories of the VTF is
attributable primarily to the particle's position in the injection
jet. Particles at the center line of each jet experience gas
temperatures tempered by their adjacent particles. Particles at the
edges of the jets experience untempered gas (flame)
temperatures.
[0089] The ARLF, by comparison, has a relatively even
time-temperature history and has a well defined processing zone
with a generally uniform temperature. The ARLF may enhance uniform
processing histories and with or without cooling of the furnace
walls.
[0090] The furnaces described above may have a burner that provides
enhanced gas streams. With reference to FIG. 12B, a burner 1208
(e.g., a commercial burner) may be disposed at the top of furnace
1200. A separate combustion unit may perform the combustion
process. The furnace 1200 of FIG. 12B may limit or reduce the
variability of processing temperatures of processed particles 1231
based on the position of the particles in the flame.
[0091] Additionally, because the combustion products (flue gas)
1237 enter furnace 1200 after thermal expansion, furnace 1200 may
not need an expansion section. Thus, a processing chamber 1205 of
the furnace may have a generally uniform cross section along the
length of furnace 1200. In some embodiments, the burner 1208 may be
operated slightly rich. Transport air 1234 used to deliver
particles 1231 to furnace 1200 functions as secondary air and may
fully complete the combustion process and may help minimize
pollutants, such as NOx.
[0092] Optionally, furnace 1200 may have a structure configured to
direct the flows therein. For example, furnace 1200 may have one or
more flow straighteners 1210 for directing the flow of the
combustion byproducts, solids, and/or secondary air. Flow
straightener 1210 may comprise a plurality of fins, a plurality of
flow channels, and the like. The illustrated flow straightener 1210
is proximate to the ports of a delivery system 1215 for injecting
solids and secondary air into the furnace.
[0093] The furnace may be configured to limit or reduce the amount
of heat lost by the combustion byproducts. The passage extending
between the combustion unit and the mixing chamber may be insulated
with any suitable insulating material. Thus, combustion byproducts
at high temperatures may be delivered and mixed with the solids and
combustion products.
[0094] In some embodiments, delivery system 1215 may deliver solids
without secondary combustion air. For example, delivery system 1215
may deliver only solids 1231 to the mixing chamber. Solids 1231 may
drop by gravity through furnace 1200. In some embodiments, delivery
system 1215 delivers solids 1231 and a transport fluid to increase
the mass flow rate of the bulk flow.
[0095] A furnace may have a flow system that includes one or more
surfaces that may repel the solids to reduce or limit wall impact.
The furnace may have a surface that is charged with an electric
potential. For example, the entire inner surface of the furnace may
be charged with a high electric potential. The particles may be
charged so that the particles are repelled from the inner wall.
[0096] The particles may comprise ingredients which render the
particles electrically conductive. In some embodiments, the furnace
inlet system may charge the particles before the particles are
delivered into the combustion chamber defined by the charged walls,
or other structures of the furnace. The inlet system may comprise
pipework. The particles may contact the walls of the pipework and
be charged. The charged particles and the walls may have like
charges so that the particles are repelled from the walls of the
furnace. Thus, the flow system may limit or prevent particle
impacts to the furnace walls. In some embodiments, the outer wall
of the furnace is charged to repel the particles. Thus, the inner
and/or the outer wall of the furnace may be charged to prevent wall
impacts. Other components of the furnace may also be charged to
repel the particles in a like manner.
[0097] The furnace may employ the Volta's hailstorm principle to
achieve a desired particle flow. A voltage may be applied between
two plates (e.g., two parallel plates) and particles may be moved
from one plate to the other. A plurality of plates or other
structures of the furnace may be positioned with respect to the
combustion chamber to cause the desired flow field of particles. In
some embodiments, an anode comprises the inlet system (e.g., the
inlet pipework) and the inner column, and the cathode may comprise
one or more collection plates downstream of the quench air
introduction system. The anode and cathode may cooperate to direct
the charged particles along desired flow paths. Additionally, the
furnace may or may not have a cyclone system.
[0098] FIGS. 13 and 14 illustrate a system having a spray dryer
1351 and a furnace 1300. A dryer may be integrated with the
furnaces described herein. The dryer may be spray dryer or other
suitable apparatus for drying material. The illustrated single unit
system may reduce the amount of structural support framework and
the need for powder transport system(s), which may be employed in
conventional systems.
[0099] The spray dryer 1351 has an output that delivers material
directly into furnace 1300. A mounting system may connect spray
dryer 1351 and furnace 1300, illustrated as an ARLF furnace. The
mounting system comprises a rotary airlock 1352, feeding cone 1350,
and funnel 1313. The rotary airlock 1352 extends from spray dryer
1351 to feeding cone 1350. Feeding cone 1350 (e.g., a vibratory
feeding cone) is connected to annular funnel 1313, which feeds
material into furnace 1300.
[0100] FIGS. 15A-B, 16, and 17 show processing system having a
drying unit and furnace combined in a single unit 1500. Slurry 1531
is delivered, preferably sprayed, through a feed inlet (FIGS. 16A
and 16B) into top chamber 1503 along with hot gases for drying the
precursor. The dry precursor falls into lower processing chamber
1504. Hot gases from a burner 1508 flow in the opposite direction
as the falling precursor. The illustrated hot gases flow upwardly
and the precursor flows downwardly through the chamber. The hot
gases from burner 1508 sweep particles outwardly and upwardly while
simultaneously processing the particles. The particles are then
cooled. The cooled particles are delivered to a cyclone 1656, where
the product is separated and the hot flue gases are returned to the
upper chamber for use in drying the slurry.
[0101] With respect to FIG. 18, a gas control circuit may control
the air/fuel mixture within the furnace. The gas control circuit
removes heat from the walls of the furnace and uses the heat for
the preheat process. Efficiency may be increased by increasing the
amount of heat removed from the walls of the furnace and fed back
into the furnace as preheat.
[0102] In some embodiments, minimal or no heat is removed from the
combustion air to reduce occurrences of pre-ignition of the air/gas
mixture. The air for the main burner serves as transport air for
the precursor. The mixing of the transport air and precursor may
reduce the air temperature while preheating the precursor
material.
[0103] When the precursor material is increased and the air/gas mix
is decreased for the same level of heat recovery, the furnace may
achieve a maximum thermal efficiency, lowest flame temperatures
and, hence, the lowest NOx levels.
[0104] Optionally, ring burner air may be passed through a cross
flow heat exchanger. The cross flow heat exchanger may exchange
heat between the ring burner air and the air/precursor mixture,
which is flowing to the main burner. Natural gas may be mixed with
the air in each path, preferably mixed after the air has passed
through the heat exchange stage to inhibit pre-ignition.
[0105] In another embodiment, cooling air may be heated and passed
through a heat exchanger. The main air supply and ring burner air
supply may be passed through the heat exchanger. In this manner,
cooling air requirements are separated from the combustion air
requirements.
[0106] During the post-formation process, particles may pass
through a cooling system. The cooling system may be in the form of
cooling jacket. A working fluid (e.g., water) may flow through the
cooling jacket so that heat is transferred from the particles to
the working fluid in the jacket. In some embodiments, the jacket
comprises a tubular section wrapped with coils (e.g., copper coils)
that are embedded in a housing. The housing may comprise aluminum.
Cooling fluid (e.g., chilled water) may be passed through the
copper coils to remove heat. In some embodiments, the water may
optionally be passed through a heat exchanger (e.g., a finned-tube
heat exchanger).
[0107] The working fluid of the jacket may be water. Water has a
specific heat four times greater than the specific heat of air.
Water also has a density of about a thousand times greater than the
density of air. Water as a coolant, as compared to air, may
substantially reduce the volume of fluid required to effectively
cool heated particles. Thus, the overall size of the cooling jacket
may be reduced. The working fluid of the jacket may be a
refrigerant or other suitable fluid for cooling the particles.
[0108] The volume of air and flue gases passing to the cyclone may
be reduced from approximately 7500 SCFM to 2000 SCFM, leading to
potential savings in the equipment cost of the cyclone. In some
embodiments, a furnace may process about 3.5 ton/hr of product that
requires approximately 6.7 MBTU/hr heat removal (1.96 MJ/sec) to
drop the temperature of the product and transport air from the
process temperature (1400.degree. C.) to a suitable temperature for
passing through pipework and to the cyclone (650.degree. C.). If
water is used as the coolant and the water is permitted to rise a
temperature of about 60.degree. C., then 7.85 kg/s of water (470
L/min) may sufficiently cool the product. If water is passed
through a finned tube heat exchanger in a closed loop system, and
air is used in the heat exchanger, then 6.7 MBTU/hr of heat from
that water may need to be removed. In some embodiments, about
50,000 SCFM of air may be used to cool the water.
[0109] If the water is discharged from the cooling jacket (e.g., a
single pass system), the amount of water passed through the cooling
jacket may be adjusted to achieve a desired discharge temperature
of the water. In some embodiments, cooling jacket maintains the
wall temperature of the furnace at about 700.degree. C.
[0110] The furnace may employ one or more spray cooling systems
that use fluid, such as water, that undergoes a phase change to
release heat. For example, a spray cooling system may use water,
which is heated and then releases heat as steam. The inner column
may be surrounded by one or more spray nozzles. The spray nozzles
may spray water onto the inner cylinder or column. The water may be
heated until the water reaches a vaporization temperature and then
forms steam that carries heat away from the surface of the inner
column. The heat recovery may be done via a heat exchanger to avoid
passing additional water vapor to the burners.
[0111] A porous wall vertical transport reactor (PWVTR) furnace may
include two or more vertically oriented tubes. The PWVTR furnace
1900 illustrated in FIG. 19 comprises tubes that are generally
concentric. In some embodiments, a PWVTR furnace comprises two
tubes (inner tube 1901 and outer tube 1902) that are somewhat
concentric and vertically inclined, wherein innermost tube 1901
comprises a porous material. A PWVTR furnace may be used for
heating and/or cooling of particles.
[0112] The inner tube 1901 may be subjected to a wide range of
environmental conditions. In some embodiments, inner tube 1901 may
be exposed to extreme temperatures (e.g., extreme hot and/or cold
temperatures), oxidizing, erosive elements, corrosive elements, and
combinations thereof, and the like. When PWVTR furnace 1900 is used
for heating particles, the surface of inner tube 1901 may comprise
material(s) suitable for flame support. Inner tube 1901 may
comprise one or more of the following materials: metals (e.g.,
drilled metal), polymers or plastic, ceramic (e.g., cast or drilled
ceramic), foam (e.g., open cell metallic foam or open cell ceramic
foam), combinations thereof, and the like.
[0113] Outer tube 1902 may surround inner tube 1901 and may
comprise a material that inhibits or limits the egress of gas out
of the sidewall of the furnace. Outer tube 1902 may thus form a
gas-tight shell and may be non-insulated, insulated, and/or
cooled.
[0114] An annulus opening 1913 may be formed between inner tube
1901 and outer tube 1902. Gases or vapors may be introduced through
annulus opening 1913 and may then pass through porous inner tube
1901. In some embodiments, the gas or vapor is combustible. For
example, the gas or vapor may comprise a fuel or a flammable
mixture of oxidizer and fuel. The gases or vapor may pass through
porous inner tube 1901 and may be ignited. In this manner, the fuel
is supported on the interior surface of inner tube 1901 for the
combustion process. Solids, gases and/or particulates are processed
by passing either up or down through the chamber of the operating
PWVTR furnace and may be either heated, cooled, combinations
thereof by staging in sections. For example, a first section 1903
of the PWVTR furnace may heat the particles. A second section 1904
adjacent to the first section may cool the particles. Various
combinations of stages may be employed to heat or cool the
particles as desired.
[0115] The PWVTR furnace 1900 may comprise more than two concentric
tubes. In some embodiments, a PWVTR includes four generally
concentric and vertically inclined tubes. The innermost and
outermost tubes may be constructed of a non-porous material,
whereas at least one of the intermediate tubes may be constructed
of a porous material. In some embodiments, both the intermediate
tubes comprise porous material. Gases or vapors may be introduced
into the two annuli between porous and non-porous tubes, i.e.,
outside the innermost tube and inside the outermost tube. Product
passes through the annulus of the two central tubes and receives
treatment from both surfaces.
[0116] A PWVTR may actively limit or prevent particle-to-wall
collisions, due to the rejecting forces at the wall surface. Thus,
a PWVTR is especially well suited for extreme heat or cold
applications, where product-to-wall contact is most likely to
result in sticking and/or accumulation of product on the reactors
interior walls, which may ultimately lead to operational
impairment.
[0117] Although the inventions have been disclosed in the context
of certain embodiments and examples, it will be understood by those
skilled in the art that the inventions extend beyond the
specifically disclosed embodiments to other alternative embodiments
and/or uses and obvious modifications and equivalents thereof.
Accordingly, the inventions are not intended to be limited by the
specific disclosures of preferred embodiments herein.
* * * * *