Abstract:
An evacuation system for an electric arc furnace that includes a combustion chamber downstream of the electric arc furnace, for receiving exhaust comprising gas and particulate from the electric arc furnace. The evacuation system also includes a dropout section downstream of the combustion chamber, for receiving the exhaust from the combustion chamber, for collecting the particulate, and for allowing the gas to pass through the dropout section to an exhaust duct.

Description:
BACKGROUND 
       [0001]    When scrap steel is melted in an Electric Arc Furnace (EAF), carbon monoxide (CO), as well as certain amounts of carbon, natural gas, pieces of scrap and slag, etc. are generated but may not be fully consumed in the process and are consequently vented outside the EAF. In the prior art (see  FIG. 1 ), these materials typically first enter a combustion chamber  110  where the larger pieces of particulate  150  are burned or fall out into a dropout box  120 . The remaining gases and finer particles pass out of the combustion chamber  110 , with flames, through an exhaust ducting system  130  lined with water-cooled panels  140  and then move on to the baghouse. 
         [0002]    A number of design flaws have been noted in conventional evacuation systems for EAFs. For example, some evacuation systems, such as the evacuation system  100  shown in  FIG. 1 , are too small. This increases the velocity of air movement inside the ducting, not allowing enough time for larger pieces of particulate  150  to fall out into the dropout box. Consequently, the particulate  150  can accumulate in the exhaust ducting  130 , eventually resulting in a clog, making the entire venting system ineffective. Accessing the water-cooled panels  140  and clogs, and other maintenance work in conventional evacuation systems such as system  100 , is very difficult—requiring significant effort both in terms of man-hours and effort to clean. In terms of maintenance, personnel assigned to perform routine cleaning of the evacuation system—and the dropout box  120  and exhaust ducting  130  in particular—use pneumatic jackhammers and shovels in a confined space. The labor intensity of this exercise often requires incremental, “confined space” permit applications and 12-16 hours of routine (e.g. monthly) downtime. 
         [0003]    Moreover, because EAF evacuation ducting is typically filled with flames from the EAF, conventional EAF evacuation systems typically make extensive use of water-cooled paneling  140 . This inevitably leads to water leaks, both inside and outside the ductwork, which puts increased demand on the remaining water systems within the facility to cool the necessary components. 
         [0004]    Further, the high speed of escape gases through evacuation system  100  can intensify corrosion and result in increased maintenance on ducting walls. The water-cooled panels  140  in evacuation system  100  typically last only about 18 months and can cost well over $100,000 each. Replacement of these panels can require 72-80 hours of downtime to perform, in an environment in which plant downtime translates into lost revenue. 
       SUMMARY 
       [0005]    This summary is provided to introduce a selection of concepts in a simplified form that are further described below in the Detailed Description. This summary is not intended to identify key features or essential features of the claimed subject matter, nor is it intended to be used to limit the scope of the claimed subject matter. 
         [0006]    Described herein is technology for, among other things, an evacuation system for an electric arc furnace that includes a combustion chamber downstream of the electric arc furnace, for receiving exhaust comprising gas and particulate from the electric arc furnace. The evacuation system also includes a dropout section downstream of the combustion chamber, for receiving the exhaust from the combustion chamber, for collecting the particulate, and for allowing the gas to pass through the dropout section to an exhaust duct. 
         [0007]    The dropout section may have an airspeed therethrough of less than 3100 feet per minute, and preferably less than 2100 feet per minute, and more preferably equal to or less than approximately 2050 feet per minute. 
         [0008]    The dropout section defines an internal chamber which may have a volume greater than 4000 cubic feet, and preferably greater than 5800 cubic feet, and more preferably equal to or greater than approximately 5870 cubic feet. 
         [0009]    The dropout section may include an upper portion and a lower portion. The lower portion may include an internal wall, an internal floor and a pre-fired low cement castable panel disposed along at least a portion of the floor and/or the wall. The panel may have a channel running along at least a portion of an outward-facing side thereof to allow air to pass therethrough to convectively cool the panel. 
         [0010]    The panel may be a wall panel disposed along at least a portion of the wall of the lower portion, and the lower portion of the dropout section may also include a pre-fired low cement castable floor panel disposed along at least a portion of the floor thereof. The floor panel may have a channel running along a floor-facing side and a wall-facing edge thereof that generally aligns with the channel of the wall panel so that air passes between the respective channels of the wall panel and the floor panel to convectively cool both the wall panel and the floor panel. In a preferred embodiment, the walls and floor of the lower portion of the dropout section are substantially lined with the pre-fired, low cement castable panels. In one embodiment, the upper portion of the dropout section may include a water-cooled panel disposed along at least a portion of a wall thereof. 
         [0011]    Further, the wall of the dropout section may include an air vent passing therethrough that is generally aligned with the channel of the wall panel so that air passes between ambient atmosphere outside the dropout section and the channel of the wall panel, through the air vent. 
         [0012]    The panel may also be a first floor panel disposed along at least a portion of the floor, and the lower portion of the dropout section may also include a second, pre-fired, low cement castable floor panel disposed along at least a portion of the floor of the lower portion and adjacent to the first floor panel. The second floor panel may likewise have a channel running along at least a portion of a floor-facing side thereof, which allows air to pass therethrough to convectively cool the second floor panel. The lower portion of the dropout section may also include a drainage trench disposed within the floor of the lower portion and below at least a portion of the channels of the first and second floor panels so that a fluid can pass between one or more of the channels of the floor panels and a space between the first and second floor panels and the drainage trench. The fluid may be air, such that the passage of the air between the floor panels and the drainage trench convectively cools the floor panels. The fluid may also, or alternatively, be water, such that the drainage trench drains the water away from the floor panels. 
         [0013]    In one embodiment, the dropout section may have a door sufficiently large to permit ingress and egress of a motorized skid loader into and out of the dropout section. The door may include a water-cooled panel disposed on an inward-facing side thereof. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0014]    The accompanying drawings, which are incorporated in and form a part of this specification, illustrate embodiments of the invention and, together with the description, serve to explain the principles of embodiments of the invention: 
           [0015]      FIG. 1  is a cross-sectional view of a conventional electric arc furnace direct evacuation system; 
           [0016]      FIG. 2  is a cross-sectional view of an improved electric arc furnace direct evacuation system, in accordance with various embodiments of the present invention; 
           [0017]      FIG. 3  is a perspective view of a lower portion of a dropout section of the improved electric arc furnace direct evacuation system of  FIG. 2 , in accordance with various embodiments of the present invention; 
           [0018]      FIG. 4  is a plan view of a lower portion of a dropout section of the improved electric arc furnace direct evacuation system of  FIG. 2 , in accordance with various embodiments of the present invention; 
           [0019]      FIG. 5A  is a first perspective view of a cement wall panel for a dropout section of an electric arc furnace direct evacuation system, in accordance with various embodiments of the present invention; 
           [0020]      FIG. 5B  is a second perspective view of the cement wall panel of  FIG. 5A ; 
           [0021]      FIG. 5C  is a rear view of the cement wall panel of  FIG. 5A ; 
           [0022]      FIG. 5D  is a bottom view of the cement wall panel of  FIG. 5A ; 
           [0023]      FIG. 6A  is a first perspective view of a cement floor panel for a dropout section of an improved electric arc furnace direct evacuation system, in accordance with various embodiments of the present invention; 
           [0024]      FIG. 6B  is a second perspective view of the cement floor panel of  FIG. 6A ; 
           [0025]      FIG. 6C  is a third perspective view of the cement floor panel of  FIG. 6A ; 
           [0026]      FIG. 6D  is an end view of the cement floor panel of  FIG. 6A ; 
           [0027]      FIG. 6E  is a bottom view of the cement floor panel of  FIG. 6A ; 
           [0028]      FIG. 7A  is a cross-sectional view of a lower portion of a dropout section of an improved electric arc furnace direct evacuation system, taken along line  7 - 7  of  FIG. 4 , showing a first convective cooling flow pattern, in accordance with various embodiments of the present invention; and 
           [0029]      FIG. 7B  is a cross-sectional view of a lower portion of a dropout section of an improved electric arc furnace direct evacuation system, taken along line  7 - 7  of  FIG. 4 , showing a second convective cooling flow pattern, in accordance with various embodiments of the present invention. 
       
    
    
     DETAILED DESCRIPTION 
       [0030]    Reference will now be made in detail to the preferred embodiments of the invention, examples of which are illustrated in the accompanying drawings. While the invention will be described in conjunction with the preferred embodiments, it will be understood that they are not intended to limit the invention to these embodiments. On the contrary, the invention is intended to cover alternatives, modifications and equivalents, which may be included within the spirit and scope of the invention as defined by the claims. Furthermore, in the detailed description of the present invention, numerous specific details are set forth in order to provide a thorough understanding of the present invention. However, it will be apparent to one of ordinary skill in the art that the present invention may be practiced without these specific details. In other instances, well known methods, procedures, components, and circuits have not been described in detail as not to unnecessarily obscure certain aspects of the present invention. 
         [0031]    Generally speaking, various embodiments of the present invention provide for a direct evacuation system for an electric arc furnace (EAF) that greatly reduces or even eliminates the above-described issues with undesirable clogging in the ductwork. To that end, various embodiments provide an evacuation system that moves the EAF exhaust much more slowly through a dropout section to enable most, if not all, of the particulate to drop out into a dropout box. 
         [0032]      FIG. 2  shows a cross-sectional view of an EAF direct evacuation system  200 , in accordance with various embodiments of the present invention. System  200  includes a combustion chamber  210  that receives the exhaust, including gasses and particulate  150  (i.e. products of combustion), from an EAF. The combustion chamber  210 , or portions thereof, may be lined with one or more water-cooled panels  240 . The exhaust then passes from the combustion chamber  210  into a dropout section  220 . The dropout section  220  includes an upper portion  221  for permitting the gasses to pass therethough and a lower portion  222  defining a dropout box for collecting the particulate  150 . The exhaust (now comprising little or no particulate  150 ) then passes from the dropout section  220  to exhaust ductwork  230 , which leads to the baghouse, where exhausted air is cleaned and purified for release into the atmosphere. 
         [0033]    System  200  represents a significant improvement over conventional EAF evacuation systems in that its configuration results in a significantly higher rate of particulate collection efficiency in the dropout section  220 . This is achieved by significantly reducing the speed at which the exhaust passes through the dropout section  220 , so as to permit the particulate  150  more time to drop out of the exhaust. In one embodiment, the dropout section  220  has an airspeed therethrough of less than 3100 feet per minute, and preferably less than 2100 feet per minute, and more preferably equal to or less than approximately 2050 feet per minute. This reduction in airspeed is initially accomplished by reconfiguring dropout section  220  so as increase its volume. For example, whereas the internal chambers of dropout boxes of prior EAF evacuation systems had volumes up to 3570 cubic feet, the dropout section  220  according to one embodiment may have an internal volume greater than 4000 cubic feet, and preferably greater than 5800 cubic feet, and more preferably equal to or greater than approximately 5870 cubic feet. 
         [0034]    It should be appreciated that constructing a dropout section in accordance with some of the above embodiments may present difficulties from the perspective of cooling. The ducting of conventional EAF evacuation systems principally relies upon water-cooled panels to keep the ducting cool. However, water-cooled panels are expensive and require extensive water processing systems within the plant. Moreover, the more water-cooled panels that are installed in EAF ducting, the greater the likelihood that a panel will leak and thus require plant downtime to replace. Accordingly, various embodiments of the present invention provide for a dropout section  220  configuration that significantly reduces reliance upon water-cooled panels  240 . 
         [0035]      FIGS. 3 and 4  show perspective and plan views, respectively, of the lower portion  222  of dropout section  220 , in accordance with various embodiments of the present invention. Instead of an expensive and high-maintenance water-based cooling system, the lower portion  222  of dropout section  220  utilizes a convective cooling system. To this end, the lower portion of dropout section  220  may be lined with a plurality of low cement, castable panels  270 - 271 , which include a plurality of wall panels  270  and a plurality of floor panels  271 . Preferably, the panels  270 - 271  are pre-fired so as to minimize or eliminate lengthy dryout times that would otherwise be required after the installation of a new panel  270 - 271 . 
         [0036]    By eliminating the use of water-cooled panels  240  from the lower portion of the dropout section  220 , less delicacy is needed in removing the collected particulate  150  from the dropout section  220 . For example, the particulate may be removed with a skid loader, instead of with a pneumatic jackhammer, which greatly speeds the cleaning process and therefore reduces plant downtime for cleaning and maintenance. To that end, the dropout section  220  may include one or more doors  280  (see  FIGS. 2 and 4 ) that are sufficiently large to permit ingress and egress of a skid loader into and out of the dropout section  220 . The doors  280  themselves may be water-cooled. 
         [0037]      FIGS. 5A-D  and  6 A-E illustrate various views of a wall panel  270  and a floor panel  271 , respectively, in accordance with various embodiments of the present invention. Wall panel  270  may include one or more hanger clips  276 , which cooperate with aligned hooks (not shown) on walls  260  of dropout section  220  to enable the quick installation and/or removal of the wall panel  270 . Panels  270 - 271  each include one or more channels  275  disposed along outward-facing sides thereof (i.e. the sides and/or edges facing the walls  260  or floor  265  of dropout section  220 ). As will be described further below, these channels  275  enable the convective cooling of the panels  270 - 271  and, thus, the lower portion of the dropout section  220 . 
         [0038]    As shown in  FIGS. 6A-E , the channels  275  of the floor panel  271  wrap around from a floor-facing side of the panel  271  to a wall-facing edge. It will be appreciated, however, that other configurations are possible, such as where the wall panel  270  has a channel  275  along multiple sides instead of the floor panel  271 , or where both the wall panel  270  and the floor panel  271  only have channels  275  along a single side thereof. When the panels  270 - 271  are installed into the dropout section  220 , they are preferably arranged so that the channels  275  along the wall-facing sides of the wall panels  270  generally align with the channels  275  along the wall-facing edge of the floor panels, so as to permit air to pass between the respective channels  275  of the wall panels  270  and the floor panels  271 , to convectively cool the panels  270 - 271 . 
         [0039]    To further facilitate the convective cooling of dropout section  220 , walls  260  of dropout section  220  may contain a plurality of air vents  261  (shown in  FIGS. 3 and 4 ) that are generally aligned with the channels  275  of the wall panels  270 , and the floor  265  may contain a drainage trench  290  disposed below at least some of the channels  275  of the floor panels  271 . The drainage trench  290  may lead to drainage pipe  292  (see  FIGS. 2 and 4 ), which may in turn have an air vent  294  and a water drain  296 . 
         [0040]    The drainage trench  290  and the drainage pipe  292  serve a dual purpose. They serve as a means of draining water from the dropout section  220  in the event that a water-cooled panel  240  leaks. Since adjacent floor panels  271  do not form a watertight/airtight seal, water from a leaky water-cooled panel  240  may pass through the gaps between adjacent floor panels  271 , travel through channels  275  (if necessary), and then drain through drainage trench  290 , drainage pipe  292  and water drain  296 . This structural relationship enables evacuation operations to continue, despite a leak in a water-cooled panel  240 . 
         [0041]    Drainage trench  290  and drainage pipe  292  also aid in the convective cooling of the dropout section  220 . The cross-sectional views of  FIGS. 7A  and  7 B show the lower portion of a dropout section, taken at line  7 - 7 ′ of  FIG. 4 , showing first and second convective cooling patterns, respectively, of the dropout section  220 , in accordance with various embodiments of the present invention. Specifically,  FIG. 7A  shows an “active” convective cooling pattern in which the suction from the baghouse is the primary force driving the convection. In this operation, the suction from the baghouse causes air to be drawn into vents  261 , down channels  275  of the wall panels  270 , across channels  275  of the floor panels  271 , up through spaces between adjacent floor panels  271 , and out to the baghouse through exhaust ducting  230 . Simultaneously, the baghouse also draws air into drain pipe  292  via air vent  294 , into trench  290  (denoted in  FIG. 7A  by the “arrow tail” symbol), and up through spaces (such as space  273 ) between adjacent floor panels  271 . 
         [0042]    It will be appreciated that as particulate  150  and debris collect in the dropout section  220  and begin to block the spaces between adjacent floor panels, the suction from the baghouse will become less and less of a driver for the convection. At some point, the convective cooling pattern will transition from the active, baghouse-driven pattern shown in  FIG. 7A  to the passive, natural convection pattern shown in  FIG. 7B , which is passively driven by the forces of natural convection. Accordingly, in the convection pattern of  FIG. 7B , the natural tendency of heat to rise causes air to be drawn into drain pipe  292  via air vent  294 , into trench  290 , across channels  275  of the floor panels, up channels  275  of the wall panels  270 , and out vents  261 . 
         [0043]    In the convective cooling patterns of either of  FIGS. 7A and 7B , the movement of air through the channels  275  of panels  270 - 271  provides enough cooling to maintain the panels  270 - 271  at a sufficiently low operating temperature. 
         [0044]    Thus, various embodiments provide for an EAF evacuation system that has a reconfigured dropout section that promotes a slower air speed, which not only greatly enhances particulate collection efficiency, but also increases the ease of cleaning. Both of these benefits lead to decreased downtime for maintenance and, thus, to a decrease in lost revenue. Further, the inclusion of convectively cooled, low cement castable panels in the dropout section provides additional benefits. In particular, it significantly reduces the amount of cooling water needed per square foot of dropout chamber, thereby reducing cost and risk for water leaks. The high strength of the panels also allows for faster cleaning with frontloading equipment, which is not possible with water-cooled panels due to the risk of mechanical damage. Moreover, if the panels are pre-fired, refractory dryout time is eliminated. Finally, the inclusion of an internal water drainage system permits continued operations in the event of water panel leakage. 
         [0045]    The previous description of the disclosed embodiments is provided to enable any person skilled in the art to make or use the present invention. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the generic principles defined herein may be applied to other embodiments without departing from the spirit or scope of the invention. Thus, the present invention is not intended to be limited to the embodiments shown herein but is to be accorded the widest scope consistent with the principles and novel features disclosed herein.