Abstract:
The invention provides a particulate size reduction system including a grinding chamber, a center shaft defining an axis of rotation and configured for rotational motion within the grinding chamber, a wheel assembly mounted on the center shaft and at least one swing hammer mounted on the wheel assembly. The at least one swing hammer preferably includes a base portion having a first end having a mounting portion for attachment to a wheel assembly of a material treatment system, a second end, an inboard portion proximate the mounting and an outboard portion proximate the second end. The swing hammer also preferably includes a wear pad disposed on the base portion. The wear pad preferably substantially covers a face of the base portion. The wear pad preferably extends from a point proximate the second end of the base portion toward the first end of the base portion to a location proximate the mount.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to methods and systems for material treatment, such as particulate size reduction. Particularly, the present invention is directed to methods and systems for material size reduction that are useful in coal technology. 
     2. Description of Related Art 
     In operations that use coal for fuel, finely-ground coal particles or “fines” are required for efficient operation, yielding higher combustion efficiency than stoker firing, as well as rapid response to load changes. Using coal fines for combustion has the potential for less nitrous oxide (NO x ) emissions and keeps oversized loss-on-ignition (LOI) unburned coal particles from contaminating the marketable ash byproduct of the combustion chamber. Thus, it is common practice to supply raw coal to a device, such as a pulverizer, that will reduce the size of the coal to particles within a desirable size range prior to being conveyed to the furnace for combustion. 
     Many pulverizers employ systems and methods including one or more crushing and grinding stages for breaking up the raw coal. Coal particles are reduced by the repeated crushing action of rolling or flailing elements to dust fine enough to become airborne in an air stream swept through the pulverizer. The dust particles are entrained in the air stream and carried out for combustion. 
     It should be readily apparent that the process of reducing solid coal to acceptably sized fines requires equipment of high strength and durability. Therefore, there exists a continuing need for crushing and grinding components which can reduce solid coal to acceptably sized fines in less time with greater efficiency, and in a manner which results increased wear life for those components. The present invention provides a solution for these problems. 
     SUMMARY OF THE INVENTION 
     The purpose and advantages of the present invention will be set forth in and become apparent from the description that follows. Additional advantages of the invention will be realized and attained by the methods and systems particularly pointed out in the written description and claims hereof, as well as from the appended drawings. 
     To achieve these and other advantages and in accordance with the purpose of the invention, as embodied herein, the invention includes a swing hammer for fastening on a crusher rotor assembly or wheel of a material size reducing and drying system. The crusher rotor assembly is preferably mounted on a center shaft of the system, wherein the center shaft defines an axis of rotation and is configured for rotational motion within a process chamber of the material size reducing system. 
     In accordance with one embodiment of the invention, the swing hammer is made at least in part from a ductile impact absorbing backing material defining a hammer face. Preferably, a wear resistant material is bonded to the hammer, such as to the hammer face. The backing material absorbs impact for the wear resistant material. The wear resistant material can take on a variety of forms, such as a wear pad that is formed separately and bonded to the hammer face, among others. The wear resistant material protects the softer backing material from wear during the crushing and/or drying process. 
     The hammer can be made in a variety of ways. Preferably, the hammer is made by way of a forging operation. The hammer is preferably shaped so that it fits over and within a lug on the crusher rotor. The crusher rotor may be fastened to the rotating assembly by way of a crusher rotor spacer. Both the crusher rotor and hammer may have the same size hole drilled through them. The hammer preferably has two holes per lug and the crusher rotor preferably has one hole per lug. In accordance with one embodiment, the swing hammer of the invention is attached to the crusher rotor by way of a hammer pin. The hammer pin may be held in place, for example, by a cotter pin positioned in a hole on the crusher rotor lug. 
     It is to be understood that both the foregoing general description and the following detailed description are exemplary and are intended to provide further explanation of the invention claimed. 
     The accompanying drawings, which are incorporated in and constitute part of this specification, are included to illustrate and provide a further understanding of the method and system of the invention. Together with the description, the drawings serve to explain the principles of the invention. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       So that those having ordinary skill in the art to which the present invention pertains will more readily understand how to make and use the present invention, an embodiment thereof will be described in detail with reference to the drawings, wherein: 
         FIG. 1  is a front view of an exemplary rotary coal pulverizer (duplex model) which can employ a plurality of swing hammers constructed in accordance with the present invention mounted therein. 
         FIG. 2  is a side view of the rotary coal pulverizer of  FIG. 1 , illustrating the discharge from the fan section of the pulverizer. 
         FIG. 3  is an enlarged localized partial cross-sectional view of a portion of the exemplary rotary coal pulverizer of  FIG. 1 , illustrating a prior art swing hammer positioned on the wheel assembly in the crusher section. 
         FIGS. 4(A)-4(B)  depict a first embodiment of a two-piece prior art swing hammer with a guard. 
         FIG. 5  depicts a second embodiment of a one-piece prior art swing hammer without a guard. 
         FIGS. 6(A)-6(C)  depict perspective, front and side views of a first representative embodiment of a swing hammer made in accordance with the invention, respectively. 
         FIG. 7  depicts wear performance of the prior art swing hammer depicted in  FIGS. 4(A)-4(B) , using a template. 
         FIG. 8  depicts wear performance of the swing hammer made in accordance with the invention depicted in  FIGS. 6(A)-6(C) , using a template. 
         FIG. 9  depicts a second representative embodiment of a swing hammer made in accordance with the invention. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     Reference is now made to the figures and accompanying detailed description which have been provided to illustrate exemplary embodiments of the present invention, but are not intended to limit the scope of embodiments of the present invention. Although a particular type of particulate size reduction system is shown in the figures and discussed herein, it should be readily apparent that a device or system constructed in accordance with the present invention can be employed in a variety of other systems, or other applications that do not involve coal as the raw material. In other words, the specific particulate size reduction processes illustrated herein are not vital to gaining the benefits associated with using a system constructed in accordance with the present invention. 
       FIGS. 1 and 2  illustrate the general location of a presently preferred embodiment of a swing hammer constructed in accordance with the present invention and employed in an exemplary rotary coal pulverizer  12 , from the exterior of pulverizer  12 . Pulverizer  12  is known as a horizontal type high speed coal mill and is closely based on a duplex model ATRITA® pulverizer sold commercially by Babcock Power Inc. However, this should not be interpreted as limiting the present invention in any way, as many types of pulverizing devices employ similar elements and are suitable for use with the present invention. 
     The duplex model is essentially two single models side by side. It should be readily apparent that a swing hammer constructed in accordance with the present invention may also be disposed in a single model. For purposes of ease and convenience in describing the features of the present invention, only a single side of the duplex model is discussed herein. 
     As can be seen in  FIG. 3 , pulverizer  12  includes a crusher-dryer section  14 , a grinding section  16  and a fan section  18 . A center shaft  20  extends through the pulverizer  12  and defines an axis of rotation. Thus, terms used herein, such as “radially outer” and “radially inner,” therefore refer to the relative distance in a perpendicular direction from the axis defined by center shaft  20 , while “axially inner” and “axially outer” refer to the distance along or parallel to the axis defined by center shaft  20 , wherein the “axially innermost” section in pulverizer  12  is crusher-dryer section  14 . 
     Raw coal and primary air enter the crusher-dryer section  14 . Prior art swing hammers  22  mounted on and driven by center shaft  20 , along with impact liners (not shown), operate to crush the coal against a breaker plate, a crusher block and an array of grids (not shown). High temperature primary air is used to flash dry a good deal of the surface moisture of the coal, which helps prepare the coal for combustion. As the high-temperature primary air evaporates moisture from the coal, the temperature of the coal-air mixture is reduced, which significantly reduces the risk of fires within the pulverizer. 
     When coal passes through the grid of the crusher-dryer section  14 , it enters the axially outer adjacent grinding section  16 . The major grinding components in grinding section  16  include stationary pegs  24  and clips  26  disposed on a rotating disc or wheel assembly  28 . 
       FIGS. 4(A)-4(B)  illustrate a plurality of prior art hammers  422 .  FIG. 4(A)  illustrates a plurality of prior art swing hammers  422  positioned on a wheel  490 . Wheel  490  is adapted and configured to be mounted on a center shaft of a coal pulverizer, as described herein. Two piece hammer  422  is made from a base portion  430  (such as a forging), a pad  440 , and a guard  450 .  FIG. 4(B)  illustrates a close up view of the hardened pad  440  mounted on the base portion  430 , including mounting holes  470  defined in base portion  430 . The base portion  430  is preferably made from a ductile material to absorb impact when crushing coal. The hardened pad  440  resists wear during the crushing process. The hammer guard  450  protects the softer, inboard portion  435  of base portion  430  and the bonding joint  460  that joins the pad  440  to the base portion  430 . Base portion  430  and guard  450  are rotatably mounted to wheel  490  by way of a pin or bolt  472 . A significant disadvantage of this design is that it is necessary to stock two parts—the combined base portion  430  and wear pad  440 , as well as the guard  450 . 
       FIG. 5  illustrates a second, prior art one-piece hammer  522  having a face  530  for impacting coal or other material mounted on a wheel  590  inside of a coal pulverizer. Hammer  522  is rotatably mounted to wheel  590  to pivot about an axis X. Hammer  522  is generally made as a one piece casting from a material such as Manganese steel (approximately 240 BHN) or stainless steel. A hardness rating for the cast stainless steel is not presently available. 
     While the prior art hammer depicted in  FIG. 5  does exhibit significant resistance to wear, the two piece hammer of  FIG. 4  has been found to have at least twice the wear life of the one piece hammer depicted in  FIG. 5 . This is possible due to the increased wear resistance. 
     In accordance with the invention, swing hammers are provided herein that address problems in the prior art swing hammers described above. 
     For purposes of illustration and not limitation, as embodied herein and as depicted in  FIGS. 6(A)-6(C) , a first representative embodiment of a swing hammer  622  made in accordance with the invention is depicted.  FIG. 6(A)  depicts a perspective view of hammer  622 .  FIGS. 6(B) and 6(C)  depict front and side plan views of hammer  622 , respectively. Swing hammer  622  includes a first end  631  having a mounting portion  633 , a second end  639 , an inboard portion  635  and an outboard portion  637 . As depicted, hammer  622  includes a wear pad  640  attached to a base portion  630  at joint  660 . Wear pad  640  may be attached to base portion  630  in a variety of ways, such as soldering, brazing and the like. In accordance with a preferred embodiment, wear pad  640  is attached to base portion  630  by way of a silver solder material. As with the previously presented swing hammers  422 ,  522 , hammer  622  includes a mounting portion including a mounting hole  670 . Base portion  630  and pad  640  are normally formed as a ductile forging and casting, respectively. 
     As can be seen, the wear pad  640  is significantly longer than the wear pad  440  depicted in the prior art swing hammer  422  of  FIG. 4 , and extends toward mounting hole  670 , over inboard portion  635  of swing hammer  622 . Wear pad  640  has accordingly been shown to help protect the inboard portion  635  of swing hammer, thereby eliminating the need for a separate guard (e.g.,  450 ) as in the embodiment  422  depicted in  FIGS. 4(A)-4(B) . By providing a one-piece swing hammer  622  and forming the pad material in a more wear resistant material it is possible to have a one piece swing hammer construction that is easier to install, and that is more durable than swing hammers of the prior art. 
       FIGS. 7 and 8  depict the results of wear tests of the prior art hammer  422  with guard  450  ( FIG. 7 ) as compared to a hammer  622  made in accordance with the invention ( FIG. 8 ). In each case, the hammers  422 ,  622  were operated in a coal pulverizer through six months of typical operation. As depicted in  FIG. 7 , a measuring fixture  700  having a profile  710  corresponding to an unused hammer  422  reveals significant wear of the wear pad. 
     Significantly, the length of the swing hammer was actually reduced by three-sixteenths of an inch. This is very problematic, as reduction of the length of a swing hammer significantly reduces the effectiveness of the coal pulverizer. For the particular hammer  422  depicted in  FIG. 7 , pad  440  is made from an abrasion resistant cast iron material having a Brinnell hardness (“BHN”) of about 600-650. Base portion  430  is made from steel, having a BHN of about 200-255. 
     In contrast, as depicted in  FIG. 8 , significantly less wear is shown on swing hammer  622 , when comparing swing hammer with its originally installed profile  810  defined by measuring fixture  800 . Most importantly, the length of swing hammer  622  did not change during use, thereby not leading to a decrease in the efficacy of the coal pulverizer. For the particular hammer  622  depicted in  FIG. 8 , pad  640  is made from an abrasion resistant cast iron material having a Brinnell hardness (“BHN”) of about 700-750. Base portion  430  is made from steel, having a BHN of about 200-255, as with the embodiment of  FIG. 7 . 
     As will be appreciated by those of skill in the art, the diverging results depicted in  FIGS. 7-8  are actually quite dramatic. 
     For purposes of further illustration and not limitation, a second embodiment of a swing hammer  922  made in accordance with the invention is depicted in  FIG. 9 . Swing hammer  922  includes a first end  931  having a mounting portion  933 , a second end  939 , an inboard portion  935  and an outboard portion  937 . Swing hammer  922  includes a base portion  930  which may be forged, and a wear pad  940 . A significant difference between the embodiment of  FIG. 9  and that of  FIG. 6  is that pad  940  includes an interrupted surface defined by a plurality of raised surfaces  942 ,  944 . As depicted, a first set of elongated raised surfaces  942  are provided that are oriented at an angle α with respect to a longitudinal axis L of hammer  922 . Similarly, a second set of elongated raised surfaces  944  are oriented at an angle β with respect to axis L. As depicted, the elongated raised surfaces are further oriented at a third angle γ with respect to each other. It will be appreciated that surfaces  942 ,  944  can be oriented at any angle with respect to each other and the pad  940 . 
     The embodiment of  FIG. 9  may be made from a variety of materials, as described herein. For example, the particular hammer  922  depicted in  FIG. 9  includes a forged base portion  930  made from steel, similar to the embodiments of  FIGS. 4 and 6 . The wear pad  940  may be made from a harder material, such as wear resistant cast iron. Wear pad  940  may be attached to base portion  930  in any suitable manner, such as brazing and the like. The description of materials of construction herein is considered to merely be exemplary and illustrative, and not limiting. For example, if desired, the hammers  622  and  922  depicted herein may be formed from a single material in a single forging operation. However, a two piece construction is preferred to permit portion  939  to be made from a softer, resilient material and the pad made from a high wear resistant material. Moreover, it will be appreciated that the different portions of swing hammers depicted herein may be made from a variety of techniques, such as casting, forging (e.g., ductile forging), and the like. 
     It will be appreciated that a variety of materials can be used to make the wear pad portion of swing hammers made in accordance with the invention. Suitable materials may include, for purposes of illustration only, ASTM A532 Class I, Type A Abrasion Resistant Cast Iron, 500 BHN minimum with 1.4-4% Cr and/or ASTM A532, Class II, Type B Abrasion Resistant Cast Iron, 550-600 BHN, with 14-18% Cr, among others. The base portions of hammers made in accordance with the invention may also be made from a variety of materials. Such materials may include, for example, ASTM A128 Grade A, Cast Manganese Steel, 240 BHN maximum, minimum 11% Mn and/or ASTM A743 Grades CF-8, CF-20, Cast Stainless Steel, 18-21% Cr, 8% Ni, among others. 
     Without wishing to be limited to a particular theory, it is presently believed that the texturing on the hammer pad of  FIG. 9  reduces wear by deflecting coal particles off of the hammer pad surface and exposing less pad surface area to be impacted by coal particles. As such, it is believed that the textured pad  940  helps to reduce wear on the pad surface. As will be appreciated, the depiction of raised surfaces  942 ,  944  is merely exemplary. Raised surfaces of any suitable shape may be used, such as round, triangular, rectangular and the like. Similarly, such raised surfaces may be arranged into any suitable pattern or may be arranged randomly. Similarly, an interrupted surface may be formed by forming a plurality of depressions of various shapes in pad  940  instead of or in addition to raised surfaces, as desired. 
     Although exemplary and preferred aspects and embodiments of the present invention have been described with a full set of features, it is to be understood that the disclosed system and method may be practiced successfully without the incorporation of each of those features. For example, many industries include applications that utilize raw materials that are first broken up into relatively small sized particles. Accordingly, the raw materials are fed into devices that employ one or more physical processes to reduce the size of the raw material prior to their use. A swing hammer constructed according to the present invention can be utilized for such purposes. Thus, it is to be further understood that modifications and variations may be utilized without departure from the spirit and scope of this inventive system and method, as those skilled in the art will readily understand. Such modifications and variations are considered to be within the purview and scope of the appended claims and their equivalents.