Abstract:
A cleaning apparatus for cleaning a smelt spout of a boiler is provided. The boiler includes a boiler wall defining an outlet port for discharging molten smelt and the smelt spout is positioned with respect to the outlet port so that the molten smelt is able to flow along the smelt spout. The cleaning apparatus includes a cleaning tool having a pair of cleaning blades generally aligned with respective side walls of the smelt spout and an actuating assembly configured to move the cleaning blades from a first position to a second position. The cleaning blades each engage the respective side walls of the smelt spout to dislodge hardened smelt deposits therefrom when in the cleaning blades are in the second position.

Description:
BACKGROUND 
     The invention relates to a cleaning apparatus for removing solidified smelt accumulations that block or restrict the discharge of smelt from a chemical recovery combustion chamber. More particularly, the invention relates to a cleaning apparatus and a smelt discharge assembly for removing solidified smelt accumulations from a smelt spout and from a combustion device outlet port. 
     Wood pulp for paper making is usually manufactured by a sulfate process, where wood chips are cooked in a cooking liquor (typically known as “white liquor”) containing sodium sulfide and sodium hydroxide. After cooking, the used liquor (typically known as “black liquor”) is washed out of the pulp and treated in a recovery unit where the cooking chemicals are refined. Without reclamation and reuse of the cooking chemicals, the cost of the paper-making process would be prohibitive. 
     The recovery unit typically includes boiler tubes extending along the interior of the boiler walls. Concurrently with the reclamation process, the heat from combustion process is utilized to generate process steam within the boiler tubes for generating electricity and/or for other applications. 
     During the recovery process, the black liquor is first concentrated by evaporation into a solution containing approximately 65 to 80 percent solids and the solution is sprayed into the internal volume of a chemical reduction furnace. Inside of the chemical reduction furnace, the organic materials in the black liquor are combusted by various processes such as evaporation, gasification, pyrolysis, oxidation, and reduction, thereby reducing the black liquor into a molten smelt of spent cooking chemicals. The molten smelt exits the furnace through a boiler outlet port and flows along a smelt spout to a collection tank. The boiler outlet port and the smelt spout are designed to drain the molten smelt from the internal volume of the furnace at a desired rate in order to maintain a safe smelt level within the furnace and in order to maximize the efficiency of the furnace, as will be discussed in more detail below. 
     The molten smelt exits the boiler at a temperature of approximately 1000 degrees Celsius and, upon contact with ambient air, a top layer of the smelt may cool enough to become hardened and form hardened deposits and/or a hardened crust on top of the molten smelt in the outlet opening and/or spout. Hardened smelt may obstruct the flow of the molten smelt, thereby reducing the effectiveness of the outlet port and smelt spout and causing the smelt level within the furnace to be undesirably high. Additionally, a reduced smelt flow may cause the molten smelt to remain in the smelt spout longer, thereby increasing the time that the smelt is subject to ambient temperatures and increasing the likelihood that more hardened deposits will form. Therefore, the hardened deposits may tend to form within the smelt spout at a rapid rate. 
     A high smelt level can cause a wide range of problems or undesirably low production levels. For example, a high smelt level may cause inefficient and unpredictable furnace operation, such as: a decrease in the amount of chemicals that can be recovered; a decrease in the process steam outputted from the boiler tubes; an increased emission of noxious gases such as carbon monoxide and sulfur dioxide. As another example, the hardened smelt may cause the molten smelt to splash out of the spout, thereby causing dangerous conditions for nearby workers and/or potentially causing property damage. Moreover, the smelt can build up to a dangerous level and either block furnace air ports, potentially causing the fire to be extinguished, or fill up the furnace windbox, causing serious corrosion problems or even causing smelt to pour out onto the floor adjacent the furnace. As yet another example, a high smelt level may cause a rapidly increase in temperature which may lead to a boiler explosion. 
     Typically, hardened deposits are manually dislodged from the outlet port and the spout at regular intervals. For example, workers hold a long rod with a tool attached to the distal end so as to scrape hardened deposits from the spout and/or outlet port. However, such manual rodding of the smelt spout and outlet port is inefficient, unsafe, and is a tedious, physically demanding job that may fatigue operators. Additionally, smelt spouts are cooled by water circulating in a water jacket surrounding the spout, which can become ruptured by improper rodding. A broken water jacket can result in an explosion in the furnace. Other dangers to workers include the potentially hazardous fumes from the collection tank. Furthermore, the regular intervals at which the hardened smelt must be removed causes labor costs to be undesirably high. 
     Recently, automated devices have been used to automatically, periodically scrape hardened deposits from the spout and/or outlet port. For example, U.S. Pat. No. 4,706,324, which issued Nov. 17, 1987, discloses a smelt spout cleaner that is mounted on or above the smelt spout. A housing is mounted above the smelt spout and, at regular intervals, a cleaning head assembly swings in a downward, sweeping stroke from the housing towards the spout to clean deposits from the boiler outlet port and then swings in an upward, sweeping stroke toward the housing so as to mirror the downward stroke and to clean deposits from the spout. The cleaning head assembly includes a cleaning head that enters the boiler outlet port on the downward stroke. Additionally, the cleaning head assembly includes pivotable channel scraping members that each has a shape and size that generally matches that of the spout. During the downward stroke, the channel scraping members each pivot into a collapsed state to ride on the top of the molten smelt flow rather than entering the flow. Then, during the upward stroke, the channel scraping members pivot back into an extended state and are scraped along the side and bottom walls of the spout. 
     However, because the width of each of the channel scraping members is generally equal to the width of the spout, the flow of molten smelt is disrupted by the scraping members during the upward stroke, thereby potentially causing the molten smelt to splash or overflow from the spout. Additionally, although the hardened smelt deposits generally only occur at the top layer of the smelt flow, the channel scraping members in the &#39;324 patent each scrape along the bottom walls of the smelt spout, thereby exposing the entire spout to potential premature wear when only select portions of the spout require regular cleaning. Furthermore, the design disclosed in the &#39;324 patent only cleans the spout along arcuate cleaning paths traveled by the scraping members so that portions of the spout that lie between the cleaning paths may remain uncleaned. Conversely, if additional scraping members are added to the design disclosed in the &#39;324 patent to minimize gaps between the cleaning paths, then the spout may be subject to unnecessary part wear. Additionally, the upward cleaning stroke lifts the hardened smelt deposits upwards and out of the smelt spout, increasing the possibility of smelt splash and/or overflow. 
     Another automated device for scraping hardened deposits from the spout and outlet port is disclosed in U.S. Pat. No. 5,542,650, which issued on Aug. 16, 1996. The &#39;650 patent discloses a cleaning head assembly that travels along a smelt spout in a direction generally parallel thereto to scrape hardened deposits from the spout walls. More specifically, the cleaning head assembly includes a plurality of U-shaped paddles that have a size and shape corresponding to that of the smelt spout so that the paddles fit within the spout and dislodge hardened deposits from the surfaces thereof as they are moved along a substantial portion of the length of the spout. 
     However, because the width of each of the paddles is generally equal to the width of the spout, the flow of molten smelt is disrupted by the paddles, thereby potentially causing the molten smelt to splash or overflow from the spout. Additionally, although the hardened smelt deposits generally only occur at the top layer of the smelt flow, the paddles each scrape along the bottom walls of the smelt spout, thereby exposing the entire spout to potential premature wear when only select portions of the spout require regular cleaning. Furthermore, because the cleaning head assembly is translated along a substantial length of the smelt spout during cleaning, the cleaning cycle may take an undesirable amount of time to complete. 
     As seen from above, it is desirous to provide an improved smelt spout assembly and a cleaning apparatus for cleaning a smelt spout to improve the efficiency and effectiveness with which a smelt spout and/or a boiler outlet port can be cleaned. 
     SUMMARY 
     In overcoming the disadvantages and drawbacks of the known technology, one aspect of the current invention provides a cleaning apparatus for cleaning a smelt spout of a combustion device so that molten smelt is able to flow from the combustion device along a flow path of the smelt spout. The apparatus includes a cleaning tool having a pair of blades that are generally aligned with side walls of the smelt spout, and an actuating assembly that moves the cleaning blades from a retracted position to an extended position to dislodge the hardened smelt deposit from the side walls of the smelt spout. 
     In one design, the cleaning blades are elongate blades. Additionally, the blades each preferably extend substantially completely along the length of the smelt spout. The blades are also preferably planar and each preferably has a relatively small thickness so as to permit the molten smelt to flow along the smelt spout substantially unobstructed. 
     In another design, the cleaning blades move along a cleaning path from the retracted position to the extended position, and the cleaning path and a normal line that is generally perpendicular to the flow path define a cleaning angle therebetween that is less than or equal to 60 degrees. As a more specific example, the cleaning angle is less than or equal to 45 degrees. The cleaning path is also preferably generally linear. 
     In one design, the apparatus includes a support assembly, such as a hood, connected to the smelt spout and the cleaning tool to permit the movement of the cleaning tool from the retracted position to the extended position. Additionally, hood preferably includes a pair of hood side walls each connected to the smelt spout and each positioned adjacent to one of the cleaning blades. The hood further includes a pair of connection assemblies each slidably coupling one of the cleaning blades with one of the hood side walls. For example, the connection assemblies each include a support rod and a sleeve slidably receiving the support rod to slidably couple the one of the cleaning blades and the hood side walls. 
     In another design, the smelt spout includes a collar portion positioned within the boiler wall outlet port and the cleaning tool includes a front portion adapted to slide along a surface of the smelt spout collar portion to remove hardened smelt deposits therefrom. 
     In another aspect of the present invention, a smelt discharge assembly is provided for facilitating the removal of molten smelt from a combustion device, including: a smelt spout having a pair of side walls and a bottom wall defining a trough, a cleaning tool movable along a cleaning path from a retracted position to an extended position to dislodge a hardened smelt deposit from the side walls of the smelt spout, and an actuating assembly configured to move the cleaning blades along the cleaning path. 
     The above configurations of the present invention provide an improved smelt spout assembly and apparatus for cleaning a smelt spout, thereby potentially improving the efficiency and the overall effectiveness with which a smelt spout and/or a boiler outlet port can be cleaned 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1   a  is a side view of a smelt discharge assembly according the principles of the present invention, having a smelt spout connected to a boiler wall and a cleaning tool for dislodging hardened smelt from the smelt spout, where the cleaning tool is in a retracted position; 
         FIG. 1   b  is a side view of the smelt discharge assembly shown in  FIG. 1   a,  where the cleaning tool is in an extended position; 
         FIG. 2  is a rear view of the smelt discharge assembly shown from line  2 - 2  in  FIG. 1   a;    
         FIG. 3   a  is a cross-sectional view taken along line  3 - 3  in  FIG. 2 , where the cleaning tool is in the retracted position; 
         FIG. 3   b  is a cross-sectional view taken along line  3 - 3  in  FIG. 2 , where the cleaning tool is in the extended position; 
         FIG. 4   a  is a cross-sectional view taken along line  4   a - 4   a  in  FIG. 3   a,  where the cleaning tool is in the retracted position; 
         FIG. 4   b  is a cross-sectional view taken along line  4   b - 4   b  in  FIG. 3   b,  where the cleaning tool is in the extended position; 
         FIG. 5   a  is a cross-sectional view taken along line  5   a - 5   a  in  FIG. 3   a,  where the cleaning tool is in the retracted position; and 
         FIG. 5   b  is a cross-sectional view taken along line  5   b - 5   b  in  FIG. 3   b,  where the cleaning tool is in the extended position. 
     
    
    
     DETAILED DESCRIPTION 
     Referring now to the present invention,  FIG. 1   a  is a smelt discharge assembly  10  according the principles of the present invention, having a smelt spout  12  connected to a boiler  14  and a cleaning apparatus  15  for cleaning the smelt spout  12 . The cleaning apparatus  15  generally includes: a cleaning tool  16  connected to the smelt spout  12  for dislodging hardened smelt from the smelt spout  12 ; a hood  52  for supporting the cleaning tool and providing protection from splashing molten smelt; and an actuating mechanism  116  for moving the cleaning tool  16  between a retracted position  16   a  (shown in  FIGS. 1   a,    2 ,  3   a,    4   a,  and  5   a ) and an extended position  16   b  (shown in  FIGS. 1   b,    3   b,    4   b,  and  5   b ) for dislodging the hardened smelt deposits from the smelt spout  12 . 
     The boiler  14  is a combustion device, such as a chemical recovery furnace, that drains recycled byproducts, such as molten smelt  18 , from an internal volume  20  of the boiler  14  to a collection tank (not shown) via the smelt spout  12 . The boiler internal volume  20  is defined by boiler side walls  22  having generally vertical steam tubes (not shown) that capture and utilize heat energy from the boiler internal volume  20  and by a generally horizontal boiler bottom wall  24  that intersects the boiler side wall  22  adjacent to a point where the smelt spout  12  is mounted so that the molten smelt  18  is able to flow into the smelt spout  12 . The smelt spout  12  is secured to the boiler  14  by a mounting plate  26  and is in fluid connection with the boiler internal volume  20  via an outlet port  28  formed in the boiler side wall  22 . 
     The smelt spout  12  includes a collar  30  extending through the outlet port  28  and a trough  32  connected to the collar  30  and extending away therefrom towards the collection tank. The collar  30  preferably has an annular ring shape and is fluidly connected to the boiler internal volume  20  to minimize potential damage from smelt splashing or overflow to the following: the boiler side wall outlet port  28 , another other nearby component, or a nearby worker. More specifically, the collar  30  preferably defines a generally oval-shaped passageway  34  (as best shown in  FIG. 2 ) so as to matingly fit within industry-standard boiler openings. Additionally, the oval-shaped passageway  34  preferably has an increasing diameter in a direction extending away from the boiler internal volume  20  so as to improve the accessibility of the collar  30  during cleaning, as will be discussed in more detail below. Alternatively, the present invention may be used in conjunction with a smelt spout having a trough that receives molten smelt directly from a boiler outlet port, rather than from a collar that is received within the boiler outlet port. 
     The trough  32  of the smelt spout extends away from the collar  30  at a downward slope so that gravitational forces cause the molten smelt  18  to flow towards the collection tank. Unlike the collar  30 , the trough  32  is preferably open along the top thereof so that the molten smelt  18  is accessible while flowing through the smelt spout  12 . This configuration is particularly advantageous for cleaning the trough  32 , as will be discussed further below. The trough  32  preferably has a U-shaped cross section defined by a pair of side walls  36 ,  38  and a bottom wall  40  so that the opening along the top of the smelt spout  12  is at least as wide as the widest portion of the trough  32  to further improve access to the molten smelt  18 . Although the smelt spout  12  shown in the figures is a single, unitary component, it may be formed from several components that are fastened together or unitarily formed with each other. 
     When the molten smelt  18  exits the internal volume  20  of the boiler  14  and is exposed to ambient air, the molten smelt  18  cools and may become hardened. For example, hardened deposits  42  (as best shown in  FIGS. 3   a,    4   a,  and  5   a ) may form on the surfaces of the smelt spout  12  and/or on top of the molten smelt  18  flowing down the smelt spout  12 . More specifically, the hardened deposits  42  typically form as isolated deposits on the upper surfaces of the smelt spout  12  where the molten smelt  18  reached its highest point. Additionally, these isolated deposits often become fused with a crust-like top layer that bridges across the smelt spout  12  between the side walls  36 ,  38  thereof. The hardened deposits  42  generally obstruct and/or reduce flow of the molten smelt  18 , thereby reducing the effectiveness of the boiler  14  as discussed above. 
     Although it is desirable to maintain the molten smelt  18  at a relatively high temperature within the smelt spout  12  to minimize the formation of the hardened deposits  42 , it is also undesirable for the smelt spout  12  to become overheated. Therefore, a water jacket  44  is present within the smelt spout  12  to maintain a desired internal temperature. The water jacket  44  shown in the figures includes an inlet  46  near the top of the smelt spout  12 , an outlet  48  near the lower end of the smelt spout  12 , and a network of cooling ducts  50  (best shown in  FIGS. 3   a - 5   b ) transporting the a cooling fluid therebetween. More specifically, the cooling ducts  50  are formed by internal surfaces of the smelt spout  12  in the smelt spout collar  30  and trough  32 . The inlet  46  is supplied with a continuous supply of relatively cool fluid, such as water. The cooling ducts  50  may be present within any portion of the smelt spout  12  that is subject to high temperatures, or they may be limited to the lower surfaces thereof so as to maintain a relatively high temperature in the portions of the smelt spout  12  that typically develop hardened deposits  42 . 
     As mentioned above, the cleaning tool  16  is connected to the smelt spout  12  for dislodging hardened smelt from the smelt spout  12 . The cleaning tool  16  is movably coupled with the smelt spout  12  via a support assembly, such as the hood  52 , that is connected to the smelt spout  12 , as will be discussed in more detail below. As best shown in  FIGS. 2-5   b,  the cleaning tool  16  includes a pair of elongate blades  54 ,  56  for removing hardened deposits from the smelt spout trough  32  and a front portion, such as a generally arcuate punch  58 , for removing hardened deposits from the smelt spout collar  30 . 
     The blades  54 ,  56  are relatively large sheets that each are aligned with respective side walls  36 ,  38  of the smelt spout trough  32  and extend therealong. More specifically, the blades  54 ,  56  are each aligned with respective side walls  36 ,  38  of the smelt spout trough  32  so as to slide along the side walls  36 ,  38  when the cleaning tool is moved into the extended position  16   b.  Additionally, the blades  54 ,  56  are each preferably relatively large, planar blades made from sheet metal. The blades  54 ,  56  are coupled with each other via one or more bridge portions  60  ( FIG. 2 ) so as to move in unison between the retracted and extended positions  16   a,    16   b.    
     The blades  54 ,  56  each have a cleaning edge  62 ,  64  for dislodging the hardened deposits  42  from the respective side walls  36 ,  38  of the trough  32 . More specifically, the cleaning edges  62 ,  64  are designed to shear the hardened deposits  42  from the side walls  36 ,  38  so that the hardened deposits  42  are permitted to flow with the molten smelt  18  down the trough  32 . The cleaning edges  62 ,  64  are preferably formed from a hardened metal that is capable of maintaining its properties throughout frequent exposure to molten materials. Additionally, although the cleaning edges  62 ,  64  shown in the figures are generally square edges, they may alternatively have a tapered shape or any other suitable design. 
     The cleaning edges  62 ,  64  of the blades  54 ,  56  each preferably extend substantially completely along a length  72  of the smelt spout  12  so that the hardened deposits  42  can be removed in a single stroke of the cleaning tool  16 , thereby reducing the time required to clean the smelt spout  12 . More specifically, the cleaning edges  62 ,  64  each preferably extend substantially completely along a flow path  73  of the molten smelt  18  between the boiler  14  and the collection tank. 
     As best shown in  FIGS. 4   a  and  4   b,  each of the cleaning edges  62 ,  64  of the blades  54 ,  56  has a thickness  74 ,  76  that is substantially small enough so that the flow of molten smelt  18  is substantially uninterrupted by the cleaning edges  62 ,  64  when the cleaning tool is in the extended position  16   b.  For example, the blade thicknesses  74 ,  76  are each so small that an effective width  77  ( FIG. 4   b ) of the trough  32  when the cleaning tool  16  is in the extended position  16   b  is only slightly smaller than an actual width  78  of the trough  32 . For example, the respective thicknesses  74 ,  76  of the cleaning edges  62 ,  64  are each preferably between 2 and 4 millimeters and the width  78  of the trough  32  is typically between 100 and 200 millimeters. 
     Referring back to  FIGS. 1-3   b,    5   a,  and  5   b,  the punch  58  is a metal sheet having a generally horseshoe shaped cross-section matching that of the smelt spout collar  30  so as to remove the hardened deposits  42  therefrom. More specifically, the outer surface of the punch  58  slides along the inner surface of the collar  30  as the cleaning tool  16  moves into the extended position  16   b.  A bottom portion  70  of the punch  58  includes a gap between respective sides of the punch  58  (best shown in  FIG. 5   b ) so as to permit the molten smelt  18  to flow along the smelt spout  12  unobstructed. The punch  58  is connected to each of the blades  54 ,  56  via fasteners  68 , or any other appropriate connection means, so that the blades  54 ,  56  and the punch  58  move in unison with each other between the retracted and extended positions  16   a,    16   b.  Alternatively, the blades  54 ,  56  and the punch  58  may be formed of a single, unitary component. 
     Similarly to the blades  54 ,  56 , the punch  58  includes a cleaning edge  66  designed to shear the hardened deposits  42  from the walls of the collar  30  so that the hardened deposits  42  flow with the molten smelt  18  along the smelt spout  12  and into the collection tank. The cleaning edge  66  is therefore preferably formed from a hardened metal that is capable of maintaining its properties throughout frequent exposure to molten materials. The cleaning edge  66  may have any suitable shape such as a tapered or a squared design. 
     As mentioned above, the cleaning tool  16  is movable from the retracted position  16   a  (shown in  FIGS. 1   a,    2 ,  3   a,    4   a,  and  5   a ) to then extended position  16   b  (shown in  FIGS. 1   b,    3   b,    4   b,  and  5   b ) for dislodging hardened smelt deposits from the smelt spout  12 . When the cleaning tool  16  is moved into the extended position  16   b,  the hardened deposits  42  (shown in  FIGS. 1   a,    2 ,  3   a,    4   a,  and  5   a ) are sheared from the surfaces of the smelt spout  12  and driven downward into the molten smelt  18 . The deposits  42  that are driven into the molten smelt  18  flow down the smelt spout  12 . Additionally, any additional deposits  42  that bridged the width of the smelt spout  12  are left unattached to the smelt spout  12  and are free to flow down the smelt spout  12 . Some or all of the deposits  42  may become molten after rejoining the flow of the molten smelt  18 . It may be desirable to clean the smelt spout  12  frequently enough to prevent or substantially prevent hardened deposits from bridging the width of the smelt spout  12 . Alternatively, it may be desirable to manually urge the loosened deposits down the smelt spout  12  after they have been dislodged from the smelt spout surfaces. 
     As also mentioned above, the hood  52  movably couples the cleaning tool  16  with the smelt spout  12  so that the cleaning tool  16  is movable between the retracted position  16   a  and the extended position  16   b.  The hood  52  includes a pair of side walls  80 ,  82  that are each connected to the respective sides of the trough  32  and that each extend generally parallel to the blades  54 ,  56  so that the outboard side or each blade  54 ,  56  engages the inboard side of the respective side wall  80 ,  82 . More specifically, each of the side walls  80 ,  82  have a horizontal connection flange  88 ,  90  extending along the length thereof and each side wall  36 ,  38  of the trough  32  has a corresponding connecting flange  84 ,  86  extending along the length thereof. The respective sets of connection flanges  84 ,  88  and  86 ,  90  are connected with each other via appropriate connection means such as fasteners, clamps, or welding. 
     A safety wall may connect the hood side walls  80 ,  82  along a top  85  and/or a back  87  of the hood  52 . The safety wall provides stability to the hood  52  and/or provides protection against smelt splashing and/or accidental access to the smelt spout  12 . The safety wall may be movably connected to the hood  52  so as to permit selective access to the smelt spout  12  for inspection, maintenance, or manual smelt rodding. For example, the top  85  and/or the back  87  of the hood  52  may include a removable safety wall, a pivoting safety wall, or another suitable design granting temporary access to the smelt spout  12 . If the safety wall completely encloses the cleaning tool  16 , it may be beneficial to provide a video camera or another surveillance device to monitor the buildup of hardened smelt  42 . Alternatively, a control mechanism may be utilized to automatically actuate the cleaning tool  16  every desired time period. Alternatively, it may be advantageous to leave the back  87  of the hood  52  open to provide manual access to the smelt spout when the assembly  10  is in use. 
     The hood  52  also includes a plurality of connection assemblies  92 ,  94 ,  96 ,  98  that slidably couple the cleaning tool  16  to the hood  52 . More specifically, each of the connection assemblies  92 ,  94 ,  96 ,  98  includes a pair of base mounts  100 ,  102  that are connected to the side walls of the hood  52  and that support a rod  104  extending therebetween and a sleeve mount  106  that is connected to the blades of the cleaning tool  16  through a slot  108  in the side walls  80 ,  82  and that slidably receives the rod  104 . Alternatively, the cleaning tool  16  may be movably coupled to the hood  52  by an integral portion of the hood  52 . 
     The base mounts  100 ,  102  are each preferably metal blocks that are connected to the outboard sides of the side walls  80 ,  82  of the hood  52  and that have indentations or channels formed therein for receiving the respective rods  104 . The base mounts  100 ,  102  serve to provide a stable connection between the cleaning tool  16  and the hood  52  and to limit the distance that the cleaning tool  16  can travel, as will be discussed in further detail below. 
     The sleeve mount  106  is preferably a cylindrical shaped sleeve that has an inner surface corresponding to the outer diameter of the rod  104  and an outer surface that is connected to one of the blades  54 ,  56  via a connecting arm (not shown) that extends through the slot  108 . The sleeve mount  106  has a longitudinal length that is sufficient to prevent binding between the sleeve mount  106  and the rod  104 . Similarly, the inner surface of the sleeve mount  106  and the outer surface of the rod  104  each preferably have relatively low coefficients of friction to prevent binding. 
     The slots  108  each at least extend substantially completely between the respective base mounts  100 ,  102  to permit travel of the sleeve mount therebetween. However, the design shown in the figures have slots  108  extending from the far base mount  100  to the edge of the side walls  80 ,  82  so that the blades  54 ,  56  can be easily removed from the hood  52  during assembly and maintenance, by removing the base mounts  100 ,  102  and sliding the sleeve mounts  106  along the slots  108 . 
     The respective slots  108  and the rods  104  are preferably parallel with each other so that the sleeve mounts  106  all move in unison with each other along the same path. Therefore, the cleaning tool  16  moves along a cleaning path  110  between the retracted position  16   a  and the extended position  16   b.  The cleaning path  110  is preferably nonparallel to the flow path  73  so that the hardened deposits  42  are quickly sheared from the trough rather than being dragged therealong in a drawn-out motion. This configuration minimizes the time required to perform the cleaning operation. 
     The cleaning path  110  cooperates with the molten smelt flow path  73  to define a cleaning angle  112  between the cleaning path  110  and a normal line  113  that is generally perpendicular to the molten smelt flow path  73 . To increase the effectiveness of the cleaning tool  16 , the cleaning angle  112  is preferably less than or equal to 60 degrees. More preferably, cleaning angle  112  is preferably between less than or equal to 45 degrees. The cleaning path  110  is also preferably generally parallel with the upper surface of the collar  30  so that the outer surface of the punch  58  slides along the inner surface of the collar  30  when the cleaning tool  16  moves between the respective positions  16   a,    16   b.  the cleaning path  110  shown in the figures is linear, but the cleaning tool  16  may travel along any other suitable path, such as an arcuate cleaning path. 
     When the cleaning tool  16  moves from the retracted position  16   a  to the extended position  16   b,  the cleaning tool  16  moves in a cleaning direction  114  that is generally downward towards the trough bottom wall  40 . This configuration is desirable because the hardened deposits  42  are driven into the molten smelt  18  rather than being dragged along the top surface of the smelt flow or being lifted out of the smelt flow. For example, as the cleaning tool  16  moves downward toward the extended position  16   b,  the hardened deposits  42  are forced into the molten smelt  18  and are able to flow along the trough  32 . The hardened deposits  42  forced into the molten smelt  18  may become molten, thereby improving the flow along the smelt spout  12 . Also, the downward cleaning direction  114  minimizes smelt splash and/or overflow. 
     The side walls  36 ,  38  of the trough  32  are generally arcuate. Furthermore, the blades  54 ,  56  are positioned flat against the hood side walls  80 ,  82  so as to minimize lateral movement of the blades  54 ,  56 . Therefore, as the cleaning tool  16  moves from the retracted position  16   a  to the extended position  16   b,  the cleaning edges  62 ,  64  remain engaged with the side walls  36 ,  38  of the trough  32 , thereby deflecting inward toward each other. This configuration maximizes the scraping force on the side walls  36 ,  38  for removing the hardened deposits  42 . Although the blades  54 ,  56  may bend in a generally linear fashion so as to form gaps  37 , the gaps  37  are relatively small so that the effective width  77  of the trough  32  is not substantially diminished. Alternatively, the blades  54 ,  56  may each have a blade stiffness suitable to substantially prevent inward deflection of the blades  54 ,  56  when the cleaning tool is in the extended position  16   b  such as to remove hardened deposits  42  without deflecting. 
     Additionally, the arcuate side walls  36 ,  38  generally prevent the blades from reaching the bottom wall  40  of the trough, thereby preventing unnecessary wear to a component of the trough that does not regularly have hardened deposits  42  formed thereon and thereby minimizing the likelihood of damage to the water jacket  44 . Additionally, the base mounts  100 ,  102  are positioned such that the sleeve mount  106  abuts the lower base mount  100  when the cleaning edges  62 ,  64 ,  66  are at a desired level in the smelt spout  12 , thereby also preventing the cleaning tool  16  from contacting the smelt spout bottom walls  40 . For example, as best shown in  FIGS. 3   b  and  4   b,  the cleaning edge  62  is slightly submerged in the molten smelt  42  but does not reach the trough bottom wall  40 . 
     The smelt discharge assembly  10  further includes an actuating mechanism, such as a linear actuator in the form of a piston assembly  116  coupled with the hood  52  and the cleaning tool  16  so as to actuate the cleaning tool  16  from the retracted position  16   a  to the extended  16   b  position. The piston assembly  116  shown in the figures includes a piston body  118  attached to the hood  52  and a piston arm  120  slidably received within the piston body  118  that is attached to the cleaning tool  16 . Also, the piston assembly includes a power source  122 , such as a hydraulic or pneumatic hose that actuates the piston arm  120 . Alternatively, the actuating mechanism may include screw drive mechanism or another suitable device for controlling the position of the cleaning tool  16 . 
     It is therefore intended that the foregoing detailed description be regarded as illustrative rather than limiting, and that it be understood that it is the following claims, including all equivalents, that are intending to define the spirit and scope of this invention. More particularly, the apparatus and assembly described are merely an exemplary apparatus and assembly, and they are not intended to be limiting. Many of the steps and devices for performing the steps described above may be eliminated or replaced by alternative steps and devices.