US20070275335A1

US20070275335A1 - Furnace for heating particles

Info

Publication number: US20070275335A1
Application number: US11/440,555
Authority: US
Inventors: Giang Biscan; Charles D. Blake; Ronald W. Cresswell; Robert E. Everhart; Hamid Hojaji; Thinh Pham; Mark G. Stevens
Original assignee: James Hardie International Finance BV
Current assignee: James Hardie International Finance BV
Priority date: 2006-05-25
Filing date: 2006-05-25
Publication date: 2007-11-29

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.

Description

CROSS REFERENCE TO RELATED APPLICATION

This application claims the benefit of U.S. Provisional Patent Application No. 60/648,480, filed May 25, 2005.

BACKGROUND OF THE INVENTION

The present invention relates generally to the processing of particles and, more particularly, to a furnace for heating particles.
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

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.
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.
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.
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.
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

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:

FIG. 1A depicts a schematic view of a vertical transport furnace with cooled walls;

FIG. 1B depicts a schematic top view of the frame structure, wherein a fabric material is attached to the frame structure;

FIG. 1C depicts a schematic view of a frame structure of FIG. 1B for holding material and forming a wall of a furnace;

FIG. 2 depicts a schematic view of a vertical transport furnace with an air buffer;

FIG. 3 depicts a schematic view of another embodiment of a vertical transport furnace with an air buffer;

FIG. 4 is a schematic view of a non-vertical transport furnace;

FIG. 5 is a schematic view of an inclined furnace;

FIG. 6 is a schematic view of a furnace employing radiant energy;

FIG. 7 is a schematic view of a vortex type furnace;

FIG. 8 is a schematic view of a recirculating load type furnace;

FIG. 9 is a schematic view of an annular recirculating load type furnace;

FIG. 10A is a representation of a computer model simulation displaying the effect of annular recirculating load type furnace;

FIG. 10B is a graph representing swirl velocities at a first cross section of the computer model simulation of FIG. 10;

FIG. 10C is a graph representing swirl velocities at a second cross section of the computer model simulation of FIG. 10.

FIG. 11A displays temperature histories of particles in a vertical transport furnace;

FIG. 11B displays histories of particles in an annular recirculating load type furnace;

FIG. 12A is a schematic view of a burner system of a furnace;

FIG. 12B is a schematic view of a modified burner system of a furnace;

FIG. 13 illustrates a system having a spray dryer connected to an annular recirculating load type furnace;

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;

FIGS. 15A and 15B are schematic views of a dryer-furnace system;

FIG. 16 is a perspective view of a dryer-furnace system;

FIG. 17 is a cutaway view of the dryer-furnace system of FIG. 16;

FIG. 18 is a circuit diagram for an air/gas control system; and

FIG. 19 illustrates a vertical transport furnace having a porous wall.

DETAILED DESCRIPTION OF THE INVENTION

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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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® 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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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 CO₂laser). 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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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 μm-200 μm, 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.
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° 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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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).
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.
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° C.) to a suitable temperature for passing through pipework and to the cyclone (650° C.). If water is used as the coolant and the water is permitted to rise a temperature of about 60° 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.
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° C.
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.
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.
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.
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.
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.
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.
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.
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.

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.