Patent Grant
7413592
The present invention relates to systems, apparatus, and/or methods for use in the processing of metal bearing material (e.g., the reduction of iron bearing materials such as iron oxide using a direct reduction process).
Hearth furnaces have been manufactured for decades and present a proven technology for various purposes, including reduction of metal bearing materials. Such furnaces have been widely used in the mineral industry for drying, preheating, roasting, calcining, steel plant waste treatment, iron ore reduction, and production of metallic iron nuggets. A process to produce direct reduced iron (DRI) may involve the following generalized processing steps: feed preparation, drying, furnace charging, preheating, reduction, cooling, product discharge, and product passivation. A process to produce metallic iron nuggets may involve all of the steps for producing direct reduced iron plus a high temperature step in which the metallic iron formed is fused to form metallic iron nuggets, and the associated slag melts and segregates from the iron. In addition, a physical separation step is generally required to separate the metallic iron nuggets from the slag and furnace hearth layer after the products have cooled and solidified.
Various issues related to the design of such furnaces (e.g., those used to produce DRI or metallic iron nuggets) include, but are clearly not limited to, material handling, engineering/construction, maintenance, flue gas treatment to remove particulates and recover sensible heat, and in some cases provide it as make-up gas, hearth integrity, and overall system reliability.
One type of hearth furnace, referred to as a rotary hearth furnace (RHF) has been adapted for the production of DRI and metallic iron nuggets. Several rotary hearth furnaces have been built for DRI production. For example, one such RHF is used in the FASTMET process developed by Midrex Corporation and is described in the article “Development of the FASTMET as a New Direct Reduction Process,” by Miyagawa et al., 1998 ICSTI/IRONMAKING Conference Proceedings.
The RHF has also been used to produce metallic iron nuggets. For example, such processes include the ITmk3 process described in U.S. Pat. No. 6,036,744, to Negami et al., entitled “Method and apparatus for making metallic iron,” and also the QIP process, described in the article “New coal-based process, Hi-QIP, to produce high quality DRI for the EAF,” by Sawa et al., ISIJ International, Vol. 41 (2001).
Processing in a typical RHF operation may include forming balls, briquets, or similar agglomerates composed of a mixture of iron ore, reductants (e.g., coal anthracite, coke, etc.), various slagging constituents (e.g., lime hydrate, fluorspar, soda-ash, etc.), water, and binders (e.g., bentonite or lime hydrate). The agglomerates may be dried in a separate drying oven and charged to the hearth of the furnace in a charging zone thereof, or perhaps, wet agglomerates may be charged directly to the hearth of the furnace in the charging zone.
The hearth is rotated to carry the agglomerates from the charging zone into a preheat zone of the RHF where the temperature is increased so as to drive off most of the volatile matter from the coal and other additives. Further rotation of the hearth carries the agglomerates into a higher temperature reduction zone where the carbonaceous constituents react with the iron oxide in the agglomerates to reduce the iron therein to metallic iron. Still further rotation of the hearth carries the largely reduced agglomerates into a high temperature fusion zone of the RHF where the iron melts and fuses to form iron nuggets and the slag fuses and separates from the metallic iron. Yet further rotation of the hearth carries the charge into the cooling zone of the furnace where both the iron and slag solidify. The hearth materials are then discharged for supplementary cooling and passivation.
One will recognize that in the production of DRI, the high temperature fusion and melting zone would not be included in the RHF. Rather, the solid DRI produced in the reduction zone would be cooled, discharged, and passivated.
The RHF has various inherent limitations. For example, feed distribution to the RHF is difficult because of the difference between the annular speed of the near and far sides of the hearth. Further, the feed must be pre-dried, i.e., if RHF area has to be dedicated to drying, the remainder of the RHF area available for production of DRI is reduced.
In addition, feedstock in the form of balls are considered a favored feedstock for iron ore concentrates to be used in a direct reduction process. Such balls are inherently fragile, especially when they contain nearly 40% volume of pulverized coal. Heat treatment of such balls in a RHF is generally non-uniform, i.e., balls on the short radius of the annular hearth receive intense direct radiation from wall burners for an appreciably greater length of time than those on the outer radius.
Further, discharge of such balls from the hearth requires that they maintain their physical integrity after reduction, which is often a problem. The balls are, for example, augered off the annular hearth and breakage could lead to jamming of the rotary hearth, damage to the hearth, or damage to an auger used for such discharge.
Various other limitations of the RHF relate to its physical construction. For example, the physical arrangement of a RHF necessarily leads to the cold feed side being next to the hot discharge side resulting in congestion and material handling complications. Further, the circular arrangement makes construction difficult (e.g., refractory, side walls, burners all have to be configured in a circular design) and the center of the RHF is congested and difficult to access for maintenance. Further, the design of the RHF, due to its circular arrangement, has size limitations placed thereon (e.g., about 60 meters diameter). For example, the hearth is generally massive and as such, problems in rotating such a large hearth increase with its size.
In addition to the RHF, other types of furnaces have also been described. For example, a paired straight hearth (PSH) furnace is described in U.S. Pat. No. 6,257,879B1 to Lu et al., issued 10 Jul. 2001, entitled “Paired straight hearth (PSH) furnaces for metal oxide reduction.”
The PSH furnace generally includes a pair of straight moving hearth furnaces located side by side, each having a charging end and a discharging end. Each furnace has a train of detachable hearth sections to enable each hearth section to be removed at the discharging end of one furnace and attached at the charging end of the other furnace. In other words, charge is moved by two straight hearth furnaces from one end to the other, i.e., two parallel solid flows in opposite directions using two side-by-side parallel furnaces. The first flow includes a first feed end, a paired furnace, and a first discharge end. The second flow includes a second feed end, a paired furnace, and a second discharge end. After the charge loaded in a hearth section at the feed end of each flow passes through one of the paired furnaces, the charge is discharged, and the hearth section is moved to the feed or charging end of the other flow to receive new charge.
However, the PSH furnace also has associated problems. For example, the charging end of one of the paired furnaces is right next to the discharging end of the other paired furnace. As such, there is no separation between the hot and cold ends of the paired furnaces. Further, in the PSH furnace, it is necessary to duplicate both charge delivery and product removal systems at each end of the furnace. This requires a complicated distribution system, or, for example, doubling the charge metering system for multiple components and the blending and drying systems.
The systems, apparatus, and/or methods according to the present invention overcome one or more of the problems described herein relating to other previously used or described hearth furnace systems. One method according to the present invention for use in processing raw material (e.g., iron bearing material) includes providing a linear furnace apparatus extending along a longitudinal axis between a charging end and a discharging end, wherein the linear furnace apparatus includes at least a furnace zone positioned along the longitudinal axis. Raw material (e.g., raw material that includes an iron bearing material to be processed) is provided into one or more separate or separable containers (e.g., one or more separate or separable passive containers that lack self mobility, one or more separate or separable containers that include an underlying substructure supporting a refractory material, one or more containers that include an underlying substructure that has a floating planar bottom panel coupled to a frame portion such that the floating planar bottom panel is allowed to expand relative to the frame portion, one or more containers that includes a planar bottom panel having one or more slot openings defined therein so as to minimize warping in high temperatures, etc.) at the charging end of the linear furnace apparatus, wherein each of the separate or separable containers includes refractory material. The method further includes moving the one or more separate or separable containers through at least the furnace zone and to the discharging end of the linear furnace apparatus resulting in processed material in the one or more separate or separable containers. The processed material is discharged from the one or more separate or separable containers resulting in one or more empty containers. One or more empty containers are returned to the charging end of the linear furnace apparatus to receive further raw material.
In one embodiment, the linear furnace apparatus includes at least a preheat zone, a furnace zone (e.g., including furnace sub-zones such as a reduction zone, a fusion/melting zone, etc.), and a cooling zone (e.g., a water jacket) positioned along the longitudinal axis between the charging end and the discharging end.
In another embodiment, at least one of the preheat zone, the furnace zone, and the cooling zone is configured using multiple modular linear sections corresponding to the particular zone being configured to allow lengthening or shortening of the at least one zone along the longitudinal axis. The use of modular linear sections may also facilitate repair of the linear furnace apparatus. Further, the linear furnace apparatus may include one or more conduits that allow movement of one or more gases between one or more of the preheat zone, the furnace zone, the cooling zone, and sub-zones thereof.
In another embodiment of the method, moving the one or more separate or separable containers may be performed using a walking beam configuration (e.g., a walking beam configuration that is substantially mechanically sealed). For example, each of the one or more separate or separable containers may be supported by one or more transport beams (e.g., beams of insulating material) of the walking beam configuration as the one or more separate or separable containers are moved along the longitudinal axis of the linear furnace apparatus and through the furnace zone.
In another embodiment of the method, discharging the processed material from the one or more separate or separable containers includes tilting the one or more separate or separable containers to discharge the processed material using at least gravity.
In yet further embodiments of the method, returning the one or more empty containers to the charging end of the linear furnace apparatus may include immediately returning the one or more empty containers to the charging end of the linear furnace apparatus, returning the one or more empty containers to the charging end of the linear furnace apparatus in an upright state, and/or returning the one or more empty containers to the charging end of the linear furnace apparatus using a container return apparatus located directly below the linear furnace apparatus.
To facilitate maintenance of the systems, the method may further include removing one or more of the empty containers and replacing the one or more removed empty containers with one or more different empty containers.
A system for use in processing raw material according to the present invention is also described. The system may include one or more separate or separable containers configured to receive raw material (e.g., separate or separable containers that include refractory material). Further, the system includes a linear furnace apparatus extending along a longitudinal axis between a charging end and a discharging end. The linear furnace apparatus includes at least a furnace zone positioned along the longitudinal axis. The linear furnace apparatus is configured to move the one or more separate or separable containers (e.g., one or more separate or separable passive containers that lack self mobility) through at least the furnace zone and to the discharging end thereof for use in processing raw material received in the one or more separate or separable containers. Further, the linear furnace apparatus includes a discharge apparatus at the discharging end of the linear furnace apparatus operable to discharge processed raw material from the one or more separate or separable containers resulting in one or more empty containers (e.g., an apparatus operable to tilt the one or more separate or separable containers to discharge processed material therefrom using at least gravity). Yet further, the system includes a container return apparatus operable to return one or more empty containers to the charging end of the linear furnace apparatus to receive further raw material.
In one embodiment of the system, the linear furnace apparatus includes at least a preheat zone, a furnace zone, and a cooling zone positioned along the longitudinal axis between the charging end and the discharging end (e.g., one or more of the zones configured using multiple modular linear sections corresponding to the particular zone being configured to allow lengthening or shortening of the at least one zone along the longitudinal axis). Further, one or more of the zones may be divided into sub-zones by one or more baffle structures and one or more conduits may allow movement of one or more gases between one or more of the preheat zone, the furnace zone, the cooling zone, and sub-zones thereof.
In another embodiment of the system, the linear furnace apparatus includes a walking beam configuration (e.g., a walking beam configuration that is substantially mechanically sealed). The walking beam configuration may include one or more transport beams configured to support one or more separate or separable containers and operable to move the one or more separate or separable containers along the longitudinal axis of the linear furnace apparatus and through the furnace zone.
In yet further embodiments of the system, the container return apparatus may be operable to immediately return the one or more empty containers to the charging end of the linear furnace apparatus, the container return apparatus may be operable to return the one or more empty containers to the charging end of the linear furnace apparatus in an upright state, and/or the container return apparatus is located directly below the linear furnace apparatus.
The above summary of the present invention is not intended to describe each embodiment or every implementation of the present invention. Advantages, together with a more complete understanding of the invention, will become apparent and appreciated by referring to the following detailed description and claims taken in conjunction with the accompanying drawings.
The present invention shall generally be described with reference to
For example, the one or more zones 26 may include a feed zone 27 (e.g., a zone that provides a buffer zone ahead of high temperature zones so that containers are not inserted directly into such high temperature environments subjecting the container and the charge thereon to unacceptable thermal shock), a preheat zone 28 (e.g., a zone for drying raw material being processed or driving off undesirable volatile components of the raw material), a furnace zone 25 (e.g., reduction zone 30 and fusion/melting zone 31 operable to carry out a majority of the chemical reaction used in processing the raw material at relatively high temperatures), a cooling zone 34 (e.g., a zone used to cool resulting processed material before discharge), or any other zone necessary for performing the desired processing. One skilled in the art will recognize that any number of zones may exist between the charging end 20 and the discharging end 22 and that the zones 26 listed herein are only exemplary of the types of zones that may be used in accordance with the present invention.
The linear furnace apparatus 12 is configured to move one or more separate or separable containers 15 through at least the furnace zone 25 (e.g., reduction zone 30 and/or fusion/melting zone 31) to the discharging end 22 for use in processing the raw material received in the one or more separate or separable containers 15. The one or more separate or separable containers 15 are moved along longitudinal axis 11 of the linear furnace apparatus 12 using a container moving apparatus 24.
In addition to the linear furnace apparatus 12, the LHF system 10 includes a container return apparatus 14 operable to return one or more empty containers 15 to the charging end 20 of the linear furnace apparatus 12 to receive raw material for processing. The LHF system 10 further includes a discharge and transfer apparatus 54 at the discharging end 22 of the linear furnace apparatus 12 operable to discharge processed raw material from the one or more separate or separable containers 15 resulting in one or more empty containers 15 and provide the empty containers to the container return apparatus 14. A transfer apparatus 52 at the charging end 20 of the linear furnace apparatus 12 provides for transfer of the one or more empty containers 15 between the container return apparatus 14 and the container moving apparatus 24.
In general, and as shown in
Generally, the one or more separate or separable containers 15 may include any container configured for holding raw material to be processed by the LHF system 10. Preferably, the one or more separate or separable containers 15 include one or more separate or separable passive containers. As used herein, a passive container lacks self-mobility. For example, a passive container is one that lacks wheels or any other elements that allows the container to move on its own. For example, a wheeled cart or a wheeled container is not a passive container.
Each container 15 includes a refractory material upon which the raw material to be processed is received. The refractory material may be used to form the container (e.g., the container itself may be formed of a refractory material) and/or the container may include, for example, a supporting substructure that carries a refractory material (e.g., a refractory lined container such as with a refractory material being located or mounted within a container apparatus or a tray formed of a non-refractory material such as stainless steel).
In other words, for example, the container including the refractory material could be fabricated from a refractory material without a separate refractory material being provided in a supporting substructure. For example, the container 15 could be formed from a silicon refractory and, as such, would not need to be lined by a separate refractory material.
One embodiment of a refractory lined container or substructure is shown in
In other words, the LHF system 10 includes a system of moving a container 15 of raw material 88 for processing through the linear furnace apparatus 12 using a container moving apparatus 24 and then back to the charging end 20 using a container return apparatus 14. The components of the container return apparatus 14, the container moving apparatus 24, and the transfer apparatus 52 and 54 are such that they provide uniform and continuous support as the containers 15 are moved from the charging end 20 to the discharging end 22 and then back again to the charging end 20. As such, the containers 15 themselves may be constructed in a manner that does not require structural integrity (e.g., they are continuously supported by other apparatus as they are moved).
The supporting substructure or tray 82 may be formed from one or more different materials, such as, for example, stainless steel, carbon steel, inconel metal, or other metals, alloys, or combinations thereof, that have the required high temperature characteristics for furnace processing. Further, the tray 82 may be configured in one or more different shapes depending upon the configuration of the LHF system 10 or the configuration of one or more components thereof. For example, the container moving apparatus 24 may require that the tray 82 be of a particular configuration such that it can effectively move the container 80 along the longitudinal axis 11 of the linear furnace apparatus 12. As shown in
Like the tray 82, the refractory 84 may be formed in any configuration such that it defines the raw material receiving region 86 for receiving raw material 88 when used in conjunction with the tray 82. The refractory material may be, for example, refractory board (e.g., such as Thermotect A, Thermotect 80, or Thermotect HT available from Vesuvius USA, Bettsville, Ohio), refractory brick as shown in
As used herein, the term separate when describing containers refers to containers that are completely separated at all times. Further, as used herein, the term separable when describing containers refers to containers that are at least completely separable from each other at the charging end 20 and/or the discharging end 22 of the LHF system 10. In other words, in one embodiment, the containers include separable containers that are mechanically linked together to prevent shifting and separating from each other as they are transported through the furnace, but then completely separable at the discharging end 22 of the LHF system 10 for discharge and return to the feed end of the furnace. In another embodiment, the containers include separate containers that are completely separate at all times. However, whether completely separate at all times or completely separable only at the charging end 20 and discharging end 22, each container 15 can be discharged and returned to the charging end 20 for provision of raw material 88 therein. Further, the container 15 may be inspected and, if in a failure mode, removed and a new container 15 installed without affecting furnace operation. This is contrary to a RHF system, wherein a hearth failure requires complete shutdown of the entire system.
The technique of using containers 15, according to the present invention, in the LHF system 10 is substantially different than in a RHF system. In a RHF system, a massive refractory ring is carried on a series of tracks. It must be relatively thick to provide sufficient mass to protect the supporting tracks and bearings from the furnace temperatures. Generally, the RHF system is in continuous service and only slightly cooled as it passes through the cooling and loading zones.
In contrast, the containers in the LHF system 10 are preferably provided such that they carry a relatively thin, lightweight refractory bed that is supported in a metal container (e.g., substructure or tray as described above), at least in one embodiment of the present invention. The retention time of the container in the linear furnace apparatus 12 is relatively short, for example, only about 10 minutes in the high temperature zone for a direct reduction process (e.g., in reduction zone 30 and fusion/melting zone 31). The relatively light refractory load also results in a thermal capacity of the containers being relatively low such that they will cool rapidly in the cooling and discharging stages of a direct reduction process, and during a return to the charging end 20 of the linear furnace apparatus 12, such containers are cool enough to accept wet or dry agglomerate.
The cross-section of
The raw material 88 may be any material suitable for processing by the LHF system 10. Preferably, the raw material 88 includes an iron bearing material. In one embodiment of the present invention, the raw material 88 includes an iron bearing material (e.g., iron oxide material) and a carbonaceous material (e.g., a carbonaceous reductant such as coal, charcoal, or coke). Further, the raw material may include other additives to enhance the physical characteristics of wet or dry agglomerates (e.g., green balls prepared from the blended components) or mixtures charged in the containers and other additives to facilitate reduction of the iron oxide material and control the chemistry and physical characteristics of the associated slag phases during processing.
In other words, generally, according to the present invention, the raw material 88 fed to the LHF system 10 (e.g., to the raw material receiving region 86 defined by container 80) may be any material suitable for processing by the linear furnace apparatus 12 and is not restricted by any components listed herein. However, preferably, at least in one embodiment, the raw material 88 includes at least an iron bearing material (e.g., iron oxide material, iron ore concentrate, recyclable iron bearing material, etc.) such that metallized iron product or metallic iron nuggets are formed after a direct iron reduction process is carried out using the LHF system 10.
As will be recognized by one skilled in the art, the raw material 88 will depend at least in part upon the processing to be performed by the LHF system 10. For example, appropriate and suitable raw material will vary for the production of fired pellets, fluxed pellets, conventional DRI pellets, pre-reduction of steel plant wastes, and the production of metallic iron nuggets, as well as for products formed by other high temperature furnace applications, such as calcining of carbonate fluxes, thermal treatment of bloating clays, firing of clay-rich industrial waste products from paper mills, singly or in combination with power plant ash to produce light weight aggregate.
In yet another embodiment, according to the present invention, the raw material 88 may be any material used or operated on by a rotary hearth furnace (RHF). In other words, the same type of raw materials may be used, according to the present invention, in the LHF system 10 as used in RHF systems.
In particular, the LHF system 10 is beneficial in production of metallic iron nuggets using direct reduction processing techniques. As such, a substantial portion of the remaining description shall be with respect to the use of the LHF system 10 and any embodiments thereof for direct reduction processing. However, the present invention is not limited to only direct reduction processes, but may be used to process any other suitable raw materials.
With further reference to
For example, the transfer apparatus 52 may include one or more of the following: hydraulic or mechanical lift and pushing mechanisms, ball bearing roller transfer tables, centering and alignment guides, mechanical linkages for automatic opening and closing of charging doors, electronic sensors and actuators to control related operations. One embodiment of a transfer apparatus 52 is shown and shall be described with reference to
Generally, as shown in
At the discharge end 22, as shown in
In one embodiment, discharge of processed material from the one or more containers 15 employs the tilting of one or more containers 15 at an angle effective for allowing the processed material to slide off the containers 15 using gravity. As will be discussed further herein, the cooling zone 34 of the linear furnace apparatus 12 allows sufficient time for complete solidification of fused processed material in the form of, for example, metallic iron nuggets before they are dumped with the use of gravity, resulting in the clean discharge of processed material from the containers 15.
However, other mechanical assist devices may be used in combination with gravity if or as required to facilitate such a clean discharge of processed material. For example, vibration as well as other mechanical elements for scraping or pushing processed raw material from the containers may be used. Such mechanical assist devices may be used for removal of any material that, for example, sticks to the container before the empty container 15 is returned to the charging end 20 of the LHF system 10.
The transfer apparatus 54 also includes a container transfer device 75 for moving an empty container 15 after processed material is discharged therefrom to the container return apparatus 14. As described with reference to the container transfer device 73, the container transfer device 75 may include any transfer mechanism effective for transfer of the empty container 15 to the container return apparatus 14 and will depend, at least in part, on the general construction and relative location of the container moving apparatus 24 and the container return apparatus 14. For example, one or more various mechanisms such hydraulic or mechanical lift and pushing mechanisms, ball bearing roller transfer tables, centering and alignment guides, mechanical linkages for automatic opening and closing of doors, electronic sensors and actuators to control related operations, powered rollers, passive rollers, centering rollers, etc., may be used to perform such functionality.
In one embodiment, as generally shown in
Upon receipt of the raw material 88 into one or more separate or separable containers 15 at the charging end 20 of the linear furnace apparatus 12, the one or more containers 15 are provided to the container moving apparatus 24 for movement along longitudinal axis 11 through the one or more zones 26 of the linear furnace apparatus 12. One skilled in the art will recognize that the one or more zones 26 will depend upon the processing necessary for the raw material 88. However, generally, in one or more embodiments of the linear furnace apparatus 12, the one or more zones 26 include at least the preheat zone 28, a furnace zone 25 (e.g., one or more zones wherein a substantial portion of a chemical reaction takes place to modify the properties of the raw material, such as a reduction zone 30 and the fusion/melting zone 31), and a cooling zone 34, all positioned along the longitudinal axis 11 between the charging end 20 and the discharging end 22.
One or more of the zones 26 may be configured using multiple modular linear sections corresponding to the particular zone being configured in order to allow lengthening or shortening of the at least one zone along the longitudinal axis 11. For example, the preheat zone 28 may be lengthened by adding sections configured for preheating raw material (e.g., sections that are all constructed in substantially the same manner and configuration).
In one embodiment, the LHF system 10 is constructed with a series of identical modules with required burners, gas and air connections, off-gas ports, etc., such that the LHF system 10 may be easily constructed at effective costs. Such a modular construction will facilitate furnace repair if failures occur therein, for example, a refractory failure in one or more portions thereof.
Further, one or more of the zones 26 may be divided into sub-zones by one or more baffle structures 46. For example, the furnace zone 25, as shown in
The linear furnace apparatus 12 is a counter flow design in that the gas flow is counter to the movement of the containers 15 and process material therein. The combustion gases produced by burners 38 in all three zones 28, 30, and 31, combined with water vapor, organic volatiles, flux calcinations products, and chemical reaction products eventually exit the furnace via flue 40. In other words, discharge flue 40 is the primary process flue. In at least one embodiment of the present invention, eventually, all gases, combustion products, water vapor, volatiles from coal or fluxes, and reaction products exit the process through discharge flue 40. However, internal recycling between the principal zones of the furnace 12 (e.g., zones 28, 30, and 31) is allowed (e.g., such as with use of additional flues or conduits).
A quench chamber 47 is connected in-line with the exit flue 40 and is equipped with water sprays 49 to cool the discharge (e.g., gases) flowing therethrough. Further connected in-line with the discharge flue 40 is a pressure control valve 55 and a variable speed exhaust fan 53 that vents the cooled gases to a discharge stack 57. The variable speed exhaust fan 53 in conjunction with the pressure control valve 55, at least in this embodiment, is used to control the pressure inside the linear furnace apparatus 12 using conventional pressure sensors and feedback control technology to control the infusion of ambient air into the linear furnace apparatus 12 (e.g., with use of controller 18).
It will be clear that exhausting hot gases from the furnace apparatus 12 can be implemented in various different manners to remove particulates and recuperate heat energy. The above description is only one exemplary embodiment of providing such exhausting of the hot gases.
Yet further, the linear furnace apparatus 12 may include one or more conduits (e.g., similar to flue 40) to allow movement of one or more gases between the preheat zone 28, the furnace zone 25, or sub-zones thereof. The conduits or flues may be incorporated into the system to allow bypass of portions of the furnace gases between zones to facilitate chemical reactions.
With yet further reference to
As used herein, substantially mechanically sealed means that the only openings to the linear furnace apparatus 12 include an inlet opening into the linear furnace apparatus 12 (e.g., where a container 15 is received into the linear furnace apparatus 12 at feed zone 27) and an outlet opening at the discharge end of the furnace apparatus 12 (e.g., at the end of the cooling zone where a container is provided to the transfer apparatus 54), and that both inlet and outlet are fitted with sealed doors that are only opened as required to allow the insertion or ejection of containers from the furnace thereby minimizing infiltration of ambient air therein. For example, as described herein such inlet and outlet may include closure apparatus (e.g., see closure apparatus 129 of
Various container moving apparatus 24 may be used to move the separate or separable containers 15 through the linear furnace apparatus 12 (e.g., steel belt systems, continuous chain, rollers, linked insulated pads, walking beams, or by sliding the containers on fixed rails). In one embodiment according to the present invention, the container moving apparatus 24 includes a walking beam configuration. As used herein, the term walking beam configuration refers to any apparatus that is operable to lift and shift forward the trays or containers 15 through the linear furnace apparatus 12 along the longitudinal axis thereof.
One embodiment of such a walking beam configuration is shown and shall be described with reference to
In other words, the LHF system 10 provides for effective sealing of the linear furnace apparatus 12 to prevent the unacceptable infiltration of ambient air into one or more zones 26 thereof. Generally, as described previously herein, the linear furnace apparatus 12 is designed as a substantially mechanically sealed unit (e.g., with walking beam configuration or other transporting system being enclosed within the sealed furnace). Ingress of air is limited to the feed inlet at the charging end 20 and the outlet at the discharging end 22 of the linear furnace apparatus 12. Such inlet and outlet of the linear furnace apparatus 12 are configured to minimize the amount of ambient air reaching the interior of the zones 26. For example, various doors, curtains, or other structural impediments to the movement of air into one or more of the zones 26 are utilized at the charging end 20 and discharging end 22 of the LHF system 10.
The container return apparatus 14 used to return the empty containers 15 from the discharging end 22 to the charging end 20 of the linear furnace apparatus 12 may include any suitable transfer apparatus that accomplishes such functionality. For example, and as shown in
Preferably, the container return apparatus 14 provides for the immediate return of the one or more empty containers 15 to the charging end 20 of the linear furnace apparatus 12. As used herein, the term immediate refers to the return of the empty container 15 to the charging end 20 with no time spent at a location for additional cooling or other processing steps.
The container return apparatus 14 is also preferably configured to return the empty container 15 to the charging end 20 in an upright state. In other words, preferably, the transfer apparatus 54 provides for the transfer of the upright and emptied containers 15 (i.e., after being discharged by discharge apparatus 77) to the container return apparatus 14 in an upright state. This upright state is maintained as the empty containers 15 are moved to the charging end 20. As such, for example, refractory material lining the trays is maintained in its desired position and is not lost during return of the container to the charging end 20.
In one embodiment of the present invention, one or more of the empty containers 15 may be removed from the container return apparatus 14. The empty containers 15 may or may not be replaced with a different empty container 15. For example, the empty containers 15 may be removed as required for repair and maintenance.
As shown in
As shown generally in
One or more of the zones 26 are provided with temperature modification apparatus 38. Such temperature modification apparatus 38 may include gas burners, as shown generally in
Various processing advantages may be available using one or more embodiments of the LHF system 10 according to the present invention. Such advantages are described with respect to various steps employed for processing the raw material using the LHF system 10, with some comparison to previously available RHF systems. Further, such advantages are described with respect to direct reduction processes of iron bearing material, but may be equally applicable to other furnace processing.
Generally, a raw material is fed to the LHF system 10 in a direct reduction process. For example, the raw material may include iron ore concentrate or other iron bearing material; a carbonaceous reductant such as coals of various grades including coal, charcoal, or coke; fluxing agents such as lime or lime hydrate; a binding agent to aid agglomeration such as bentonite or lime hydrate; and water. One skilled in the art will recognize that this is an illustrative type of raw material and does not limit the types of materials with which the LHF system may be used. Further, for example, the raw material provided in the process may be in the form of green balls prepared from a blend of components such as components selected from those described above, or may be provided by providing one or more layers of a blend of one or more of such components, or of the components themselves.
The requirements for mixing and blending the desired components in proper proportions will vary depending upon other parameters required to carry out the direct reduction processing. One will recognize that any number of direct reduction processing parameters and techniques may be carried out using the LHF system 10, and that the present invention is not limited to any particular direct reduction process. Many of such processes are described in the art and as such will not be described in great detail herein. However, the various steps that may benefit from the use of the LHF system 10 shall be described.
Drying of the raw material 88 is generally necessary. For example, mixing and blending of the raw material 88 is normally performed in a wet state (e.g., the blend may contain from 5-15% moisture). If the raw material 88 is agglomerated (e.g., either formed into balls or briquettes), then the agglomerates have to be dried under carefully controlled conditions to avoid decrepitation, loss of integrity of the agglomerates, and release of excess dust.
In conventional RHF systems, normally an external system is used to form the agglomerates and the agglomerates are then transferred to the RHF furnace for direct reduction processing. Such dried agglomerates are inherently fragile and cannot be readily conveyed to feed hoppers as breakage occurs in both roller and vibrating feeders. Such breakage is generally overcome by adding excessive amounts of binders, such as bentonite, or by adding lime and using extended heat treatment to develop a carbonate bond, or by other pre-treatment methods. Such additions are costly and, also, in the case of bentonite, such additions add unwanted slagging components to the mix that require additional fluxing agents and thermal energy to process.
Charging a “green” ball (e.g., a non-dried agglomerate), compared to a dried agglomerate, is much easier. The non-dried agglomerates can absorb multiple transfers without excessive breakage or dusting and can be more easily transferred to the furnace. However, drying of such green balls in a RHF is problematic in that there is a practical limit to the hearth diameter, and, if a portion has to be reserved for drying, then it has an adverse effect on productivity related to the final product. Further, in the RHF, the hearth itself is massive and reaches very high temperatures in the final fusion zone in direct reduction processing. Such high temperatures would still be too high at the feed point in an RHF to accept wet agglomerates without excessive decrepitation.
According to the present invention, the LHF system 10 overcomes such problems of a RHF system. First, the containers 15 are designed to be comparatively light with relatively low heat capacity so that by the time they have been discharged at the discharging end 22 and returned to the charging end 20, the empty containers 15 have cooled to the point that wet agglomerate feeding of raw material 88 is acceptable.
Second, the preheat zone 28 can be easily implemented in the LHF system 10 by merely adding length to the linear furnace apparatus 12. For example, by enclosing a section of space and allowing latent heat in the containers 15 to dry the wet agglomerate provided therein, such a preheat zone may be implemented. As previously described herein, the preheat zone 28, or a drying zone, may be added in modular sections depending upon the necessary drying requirements. In other words, there are no restrictions on length of the preheat zone, unlike the RHF.
Third, drying in the preheat zone 28 may be accomplished using off-gases from one or more of the other zones 26. For example, if necessary or desirable, a portion of the hot off-gases from the direct reduction process in the furnace zone 25, or a sub-zone thereof, can be circulated through the preheat zone 28 to expedite the drying process.
With respect to the loading of the linear furnace apparatus 12, preferably, the raw material 88 provided to the furnace is distributed uniformly across the width of the furnace to achieve efficient reduction and maintain productivity. The LHF system 10 allows the use of off-the-shelf feeding components and minimizes distribution problems therein. For example, such off-the-shelf feeding components may include roller, vibrating, oscillating belt or apron belt feeders. In contrast, a RHF system must deal with the differential movement between inner and outer portions of the circular hearth that make uniform feed distribution more difficult.
The LHF system 10, according to the present invention, can duplicate any time/temperature thermal cycle currently used in a RHF system. For example, the linear furnace apparatus 12 can be divided into as many zones 26 as required (e.g., by providing various temperature differences across one or more zones, and/or by installation of optional baffle structures 46). The recycling of off-gases from one zone to another can be controlled as easily in one as the other. In other words, the thermal cycling in the preheat zone 28, reduction zone 30, and fusion/melting zone 31 for performing a direct reduction process (e.g., a metallic nugget formation process) can easily be controlled in the LHF system 10 according to the present invention.
Further, the linear furnace apparatus 12 is preferably designed such that the distribution of temperature modification apparatus 38 (e.g., gas burners) is symmetrical. This is generally shown in
At least in one embodiment, upon reduction of the raw material in the reduction zone 30, and further melting/fusion in the zone 31, a resulting processed material is provided in the container 15 as it moves into the cooling zone 34. The resulting product of the direct reduction process using the LHF system 10, whether it be a metallic iron nugget or other product resulting from a direct reduction process, in many instances, needs to be protected from re-oxidation until it is cooled enough to be handled under ambient conditions. For example, in many conventional direct reduction processes, metalized pellets are formed which are easily oxidized. Although an iron nugget direct reduction process produces a metallic iron nugget that is quite resistant to oxidation, generally, it may still be necessary to provide a cooled, processed material. Further, metallic iron nuggets formed using direct reduction processes also must be chilled enough to solidify before they can be discharged at the discharging end 22 of the linear furnace apparatus 12.
A RHF system has a cooling or chilling zone at the end of the cycle, wherein a water jacket is used to cool the processed material on a bed thereof to an acceptable level for discharge. This is an additional constraint for the RHF system because the area required for cooling has a direct effect on the area of the RHF system that can be used for producing product. Generally, product in a RHF system is discharged with minimal cooling and transferred to an external cooling system under a controlled atmosphere to prevent oxidation. In other words, cooling completely on the hearth of a RHF system is generally not practical.
Quite in contrast, the LHF system 10, according to the present invention, can be easily and economically extended to provide sufficient cooling so that the processed material can be discharged with minimal concern for re-oxidation and significantly reduce product handling problems, cost, and maintain product integrity.
If the processed material of the linear furnace apparatus 12 is conventional metalized pellets, they will generally have a tendency to re-oxidize if they come into contact with air while they are too hot. The extension of the cooling zone 34 in a LHF system 10 is relatively inexpensive. It can be lengthened to provide enough time for product to cool to the point where the resulting processed product is no longer pyrophoric. Lower product discharge temperatures also simplify downstream handling problems.
If the processed material is in the form of metallic iron nuggets, extended cooling on the hearth may be provided to allow direct screening of the product to remove slag and carbonaceous hearth material for recycling, or such cooling may be sufficient when the raw processed material is cooled to the point where water quenching may be applied.
The cooling section 34 of the linear furnace apparatus 12 may be configured in any manner such that it is suitable for performing the cooling function for the processed material passing therethrough (e.g., the length may be extended to provide adequate cooling). For example, the cooling zone 34 as shown in
Discharging processed material from a conventional RHF system is usually accomplished using, for example, a water-cooled rotary screw. If the processed material is uniformly-sized metalized pellets or briquettes and is completely solidified, a rotary screw can perform flawlessly. However, if the product contains agglomerates and if coalesced, or semi-liquid slag phases are present that will adhere to the screw or pile up on the hearth where it may cause discharge problems.
In contrast, the discharge of processed material from the containers 15, according to the present invention, may be accomplished, at least in one embodiment, by tilting the containers 15 at a high angle and allowing the processed material to slide off. By having an effective cooling zone 34 (e.g., a cooling zone not constrained in length due to the linear nature of the system), sufficient time can be allowed for complete solidification of any fused product components before the processed material is discharged, and discharge from the containers 15 can be accomplished cleanly. Also as described herein, discharge by gravity may also be combined with a mechanical assist.
The LHF system 10 provides, at least in one embodiment, the advantage of physically separating the cold feed end of the system, i.e., the charging end 20, from the hot product end of the system, i.e., the discharging end 22. The separation of these two ends of the LHF system 10 is automatic and may also provide a simple layout for a plant having such equipment. For example, the processed material from the LHF system 10 may be fed from the discharge end 22 directly to a furnace, e.g., an electric furnace, for final smelting. Such separation of the charging end 20 and discharging end 22 does not exist in a RHF system, or even the PSH system described in the Background of the Invention section herein. In a RHF system, for example, the raw material 88 and the processed material are added and discharged, respectively, from the furnace in the same region. Likewise, for example, in a PSH furnace, one discharging end is directly adjacent a charging end of another paired furnace.
The LHF system 100 is operated under control of a control system (not shown, but which may be any suitable system for controlling the functionality of the furnace) and includes a linear furnace apparatus 112 extending along a longitudinal axis 111 of the LHF system 100. The linear furnace apparatus 112 is operable to move one or more containers 115 from a charging end 120 to a discharging end 122 of the LHF system 100. A feed apparatus 113 (e.g., any suitable feed apparatus such as off-the-shelf feeders) is configured for providing a raw material 188 into the one or more containers 115 such that the raw material may be transported through the linear furnace apparatus 112. The raw material 188 is processed as the container 115 is moved by a container moving apparatus 124 of the linear furnace apparatus 112 through one or more process zones 126 to the discharging end 122 along longitudinal axis 111.
At the discharging end 122, a transfer/discharge apparatus 154 is used to discharge the processed material (e.g., by tilting and allowing gravity to discharge the processed material from the one or more containers 115) and further to transfer the empty container 115 after discharge to a container return apparatus 114. Preferably, the empty container 115 is returned in an upright position to the charging end 120. Further, preferably, the empty container 115 is provided immediately to the charging end 120 directly below the linear furnace apparatus 112. In other words, the container return apparatus 114 is positioned directly below the linear furnace apparatus 112. A transfer apparatus 152 is used to transfer the empty container 115 to a location such that it can once again be fed with raw material 188 and provided to the linear furnace apparatus 112.
As shown in
As best shown in
The mechanical arrangement for raising and lowering the beams may be different depending upon the size of the linear furnace apparatus 112 (e.g., use of hydraulic driven lift pistons or a mechanical lever arm system). Further, it may even be possible that the one or more containers 115 may be moved through the linear furnace apparatus 112 on rollers, or supported by a continuous chain by providing water-cooled jacketing for the roller supports.
The walking beam configuration shall be described in further detail with reference to
As shown in
The motion of motion beam 227 is coupled through to the walking transport beams 212 by means of walking beam coupler 229. The walking beam coupler 229 includes the rollers 224 which are configured to roll up and down wedges 220 as the walking beam operates. The rollers 224 are pivotably coupled at pivot point 225 to carrier beam 228 by support plates 233, with one end of support plates 233 being pivotably coupled at pivot point 225 to rollers 224 and the other end of the plate being fixed to carrier beam 228. A pivot coupling 231 is used for coupling the carrier beam 228 to trough 230 which defines an opening for supporting the insulated material of walking transport beams 212. A hydraulic apparatus 241 is coupled at the charging end 120 in a manner so as to move the trough 230 supporting the walking transport beams 212.
Using the motion of motion beam 227 and walking transport beams 212 as controlled by hydraulic apparatus 240 and 241, transport of containers 115 is provided along the linear path of a linear furnace apparatus 112. For example, as the wedges 220 are moved toward the charging end 120 by hydraulic apparatus 240, the walking transport beams 212 (i.e., supported by the carrier beam 228 carried by roller 224) are raised as roller 224 is rolled upon wedges 220 imparting a lift to the transport beams 212 and containers 115 coupled to trough 230 which supports the walking transport beams 212. A sequential movement by hydraulic apparatus 241 moves the transport beams 212 and containers 115 toward the discharging end 122 (e.g., 6 to 12 inches of motion). Reversing such motions utilizing the hydraulic apparatus 240 and 241 provides for the lowering of the containers 115 such that they rest upon side resting portions 213 and center beam 210 and moves the walking beams 212 toward the charging end 220 of the LHF system 100 prior to repeat of the lifting and translation cycle which moves the one or more containers 115 towards the discharging end 122.
The LHF system 100 shown in
For example, as shown in
Structure 131 of the linear furnace apparatus 112 defines an opening for allowing containers 115 to pass from the feed zone 127 into a preheat zone 128 of the linear furnace apparatus 112. Optional baffle structures 146 may be utilized to create further zones, including reduction zone 130 and fusion/melting zone 132, for processing of the raw material 188 in the one or more containers 115. In addition, such baffle structures 146 allow for the transfer of gases from one zone to another zone and also into the preheat zone 128.
As similarly described with reference to
As previously described herein, the preheat zone 128 provides for preheating or drying of wet raw material in a direct reduction process. For example, in addition to drying the material, such a preheating process dries off volatile components in the raw material 188. In this particular exemplary embodiment, the preheat zone 128 may be held at a temperature of about 1000° F. to about 2000° F. by gas burners 138 positioned therein and controlled by controller (not shown) such as through use of roof-mounted thermocouples 199. As one skilled in the art will readily recognize, various sensors may be utilized with the linear furnace apparatus 112 for use in controlling the atmosphere in the interior 261 thereof. For example, carbon dioxide, carbon monoxide, and oxygen sensors may be used to monitor and control the reducing potential of the furnace atmosphere. Further, site ports 139 may be included in one or more of the zones to provide for visual examination of the interior 261 of portions of the furnace apparatus 112.
The containers 115 are then moved along the linear path of the linear furnace apparatus 112 from the preheat zone 128 to a reduction zone 130 where a chemical reduction process occurs to reduce the raw material 188 (e.g., an iron bearing material such as iron oxide). Generally, for example, the temperature within the reduction zone 130 is maintained at a temperature in the range of about 1800° F. to about 2400° F. using controller (not shown) and one or more sensors such as thermocouples 199, and further with use of gas burners 138.
The containers 115 are then moved along the linear path of the linear furnace apparatus 112 from the preheat zone 128 to a reduction zone 130 where a chemical reduction process occurs to reduce the raw material 188 (e.g., an iron bearing material such as iron oxide). Generally, for example, the temperature within the reduction zone 130 is maintained at a temperature in the range of about 1800° F. to about 2400° F. using a controller (not shown) and one or more sensors such as thermocouples 199, and further with use of gas burners 138.
As described elsewhere herein, after formation of, for example, metallic iron nuggets in a direct reduction process, such processed material is generally cooled. As such, the one or more containers 115 are provided from the fusion/melting zone 132 to a cooling zone 134 through an opening defined by structure elements 151 extending down towards the container moving apparatus 124. The cooling zone 134 is preferably configured as a water jacket wherein water is provided to the cooling zone 134, heated through the transfer of heat from the processed raw material to the water, with the heated water being transported from the cooling zone 134. Such water jackets are readily known, available, and/or described in a variety of configurations and need not be described in further detail herein.
The one or more containers 115 are transferred from the cooling zone 134 with use of a roller assist mechanism 133. An actuated closure mechanism 135 is provided at the outlet 181 of the cooling zone 134 for preventing ambient air from entering into the zone and also preventing gases from escaping therefrom. The actuated closure mechanism 135 may be similar or different to that of actuated closure 129 and include any suitable apparatus for minimizing air or gas movement through the outlet 181.
The one or more containers 115, after processing of the raw material 188 provided therein, are transported from the cooling zone 134 to the discharge and transfer apparatus 154. The discharge and transfer apparatus 154, as shown in one exemplary embodiment, includes a transfer platform 161 (e.g., a platform comprising a plurality of ball-bearings on an upper surface thereof, as shown best in
Prior to such transfer to the container return apparatus 114, the processed material is discharged using gravity. For example, the container 115, including the processed material (e.g., metallic iron nuggets), is raised to a particular pre-determined angle 164 by hydraulic apparatus 165. The transfer platform 161 is pivotable at pivot point 163 for allowing rotation of the transfer platform 161 to angle 164. Any processed material may then be provided by gravity into a collection container 155 for use in, for example, the transfer to one or more further apparatus. One skilled in the art will recognize that various mechanical assist devices may also be used to clean the processed material from the container 115, if necessary.
After return of the empty container 115 to horizontal from angle 164, a hydraulic apparatus 167 is used to lower the transfer platform 161 to allow transfer of the empty container 115 to the return apparatus 114. The empty container 115 is then transferred to a carrier cart device 168 by rotating the transfer platform 161 to a particular angle 179 about pivot point 166. The empty container 115 is then transferred to the carrier cart device 168 using gravity with proper alignment by guide and centering blocks or rollers 169. Further, although the container 115 may be moved to the carrier cart device 168 by gravity, other mechanical assist devices (e.g., imparted cable motion, belt, or any other movement mechanism) may be used in combination to provide the container 115 to the carrier cart device 168 of the container return apparatus 114. One will recognize that although a carrier cart is used in this particular embodiment, that the container 115 may be transported to charging end 120 without a cart in one or more other embodiments of the present invention.
The container return apparatus 114 includes a return apparatus structure 185 supported upon pad 116 in addition to wall structures 187 for retaining and directing the container 115 during its return to the charging end 120 of the LHF system 100. The container return apparatus 114 further includes the carrier cart device 168 and cable apparatus including rollers 182 and cable 183 driven by a motor apparatus 196 used to impart motion to cable 183 which is attached in some manner to carrier cart device 168, and therefore is used to impart motion to the empty container 115. Using the container return apparatus 114, the container is moved towards the charging end 120 of the LHF system 100. The cable-driven apparatus may be used because of the relatively lightweight nature of the horizontal and non-self-mobile nature of the containers 115. However, one skilled in the art will recognize that a belt mechanism or any other transfer apparatus may be used to move the containers 115 (whether in a cart or alone) to the charging end (e.g., a transport apparatus that can be located and operable below the linear furnace apparatus 112).
The carrier cart device 168 may be any suitable apparatus for receiving an empty container and providing adequate support thereto during transport. For example, the cart device 168 may include one or more of the following features: a planar bottom portion coupled to the cable 183, one or more sidewalls (e.g., extending from the bottom portion) for retaining the empty container on the cart device 168 as it is transported, apparatus to assist in receiving the container 115 or moving the container to another apparatus (e.g., rollers, ball bearings, hydraulics, etc.). One will recognize that the cart device may be configured in any number of different manners, shapes and sizes, and that the present invention is not limited to any particular configuration.
Another embodiment of a carrier cart 200 that may be used according to the present invention is shown in
The set of transfer wheels 272 include a plurality of pairs of transfer wheels; each pair of transfer wheels is caffied by a floating shaft 213 that is free to move up and down (i.e., vertically) within slots 218 on opposing edges of cart frame 215 (best shown in
In this carrier cart embodiment of the present invention, as the cart 200 approaches the charging end 120 where the discharge plate 219 is located, the transfer wheels 272 ride up (e.g., preferably simultaneously) the ramps 220 to propel the container 115 forward, and off the carrier cart 200 and onto the transfer apparatus 152 to be moved to the inlet to the furnace apparatus 112. The arrows in
Generally with further reference to the configuration shown in
As shown in
One will recognize that the furnace zones are generally created in a symmetrical manner in the exemplary embodiment, such that one or more sections of such zones may be added depending upon the processing necessary for the raw material. Further, as this is a linear system, the linear path may be extended such that a longer preheat, feed, cooling, or additional furnace zones can be easily added by insertion of additional modular units configured for the functionality required.
In one embodiment, a container 115 that needs to be recycled may be removed from the transfer platform 161 at the discharging end 122 prior to its return to the charging end 120 using container return apparatus 114. In addition, various other transfer concepts to remove a container 115 and/or insert a different container in its place may be provided as modifications to the LHF system 100 at one or more various locations of the system (e.g., at the charging end 120, at the discharging end 122, or even at a location therebetween).
All patents, patent documents, and references cited herein are incorporated in their entirety as if each were incorporated separately. This invention has been described with reference to illustrative embodiments and is not meant to be construed in a limiting sense. As described previously, one skilled in the art will recognize that other various illustrative applications may use the techniques as described herein to take advantage of the beneficial characteristics of the particles generated hereby. Various modifications of the illustrative embodiments, as well as additional embodiments to the invention, will be apparent to persons skilled in the art upon reference to this description.
This application claims the benefit of U.S. Provisional Application Ser. No. 60/558,197 filed 31 Mar. 2004, which is incorporated herein by reference in its entirety.
The present invention was made with support by the Economic Development Administration, Grant No. 06-69-04501. The government may have certain rights in the invention.
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