Abstract:
The present invention is directed to, among other things, a grinding chamber side liner for attaching to the interior of a coal pulverizer housing that includes an overhanging rim for covering gaps between parts installed adjacently with respect to each other within the housing.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a grinding process for a material size reduction process based on the particle size, and more particularly, it concerns an improved grinding chamber side liner for use in a grinding section of a rotary coal pulverizer. 
     2. Background of the 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 also produces 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 range prior to being used 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 actions 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 grinding chamber components that, among other things, are able to withstand extremely harsh conditions so that the process can operate more efficiently with less downtime due to maintenance and repairs. 
     SUMMARY OF THE DISCLOSURE 
     The present invention improves upon and solves the problems associated with the prior art by providing, among other things, a grinding chamber side liner for protecting against coal flow damage. The grinding chamber side liner of the present invention includes a generally arcuate liner body defining a radially inner edge and a radially outer edge, among other things, wherein the radially inner edge includes an overhanging rim defining a shoulder adjacent thereto. 
     The grinding chamber side liner of the present invention can include a hole configured for receiving a fastening assembly to facilitate the engagement of the liner body. The liner body is preferably fabricated substantially of Ni-Hard. 
     In another embodiment, a grinding chamber side liner of the present invention can be constructed so that the thickness of the liner body gradually decreases from the radially outer edge to the radially inner edge. Alternatively, the thickness of the liner body can gradually decrease in one or more radially inner corners of the liner body. 
     The present invention is also directed to a coal pulverizer having a grinding chamber and a center shaft defining an axis of rotation and configured for rotational motion within the grinding chamber. The coal pulverizer of the present invention includes a grinding chamber side liner for attaching to the interior housing wall of the grinding chamber. This liner includes an arcuate liner body defining a radially inner edge and a radially outer edge, among other things, wherein the radially inner edge includes an overhanging rim defining a shoulder adjacent thereto. 
     The grinding chamber side liner of the present invention can include a hole configured for receiving a fastening assembly to facilitate the engagement of the liner body. The liner body is preferably fabricated substantially of Ni-Hard. 
     In another embodiment, a grinding chamber side liner of the present invention can be constructed so that the thickness of the liner body gradually decreases from the radially outer edge to the radially inner edge. Alternatively, the thickness of the liner body can gradually decrease in one or more radially inner corners of the liner body. 
     The present invention is also directed to a grinding chamber side liner for attaching to the interior housing wall of a grinding chamber adjacent to a cheek plate forming a gap therebetween that has a body which includes a portion for covering the gap. The body can be arcuate and define a radially inner edge and a radially outer edge, and the radially inner edge can include an overhanging rim that defines a shoulder adjacent thereto for fitting adjacent the cheek plate and covering the gap formed between the liner and cheek plate. 
     These and other aspects of the present invention will become more readily apparent to those having ordinary skill in the art from the following detailed description of the invention taken in conjunction with the drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE FIGURES 
       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 front view of an exemplary rotary coal pulverizer (duplex model) which can employ a grinding chamber side liner constructed in accordance with the present invention therein mounted on the center shaft at two locations; 
         FIG. 2  is a side view of the rotary coal pulverizer of  FIG. 1 , illustrating the output 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 grinding chamber side liner abutting the grinding chamber interior walls in the grinding section; 
         FIG. 4  is a perspective view illustrating a prior art grinding chamber side liner; 
         FIG. 5  is a partial perspective view of a prior art grinding chamber side liner installed adjacent a cheek plate in the grinding chamber of a coal pulverizer; 
         FIG. 6  is a perspective view of a grinding chamber side liner constructed in accordance with the present invention; 
         FIG. 7  is a front view of the grinding chamber side liner shown in  FIG. 6  constructed in accordance with the present invention; 
         FIG. 8  is a front view of another embodiment of a grinding chamber side liner constructed in accordance with the present invention, illustrating a liner that differs in shape and cross sectional thickness as compared to the embodiment shown in  FIG. 6 ; 
         FIG. 9  is a front view of another embodiment of a grinding chamber side liner constructed in accordance with the present invention illustrating another liner that differs in shape and cross sectional thickness as compared to the embodiment shown in  FIGS.6 and 8 ; 
         FIG. 10  is a cross sectional view of the liner shown in  FIG. 6 , illustrating the overhanging rim and shoulder and reduction in cross sectional thickness at the radially inner edge; 
         FIG. 11  is a cross sectional view of the liner shown in  FIG. 8 , illustrating the overhanging rim and shoulder and reduction in cross sectional thickness at the radially inner edge; 
         FIG. 12  is a cross sectional view of the liner shown in  FIG. 9 , illustrating the overhanging rim and shoulder and reduction in cross sectional thickness at the radially inner edge; 
         FIG. 13  is a partial front view of the liner shown in  FIG. 6  installed adjacent a cheek plate in the grinding chamber of a coal pulverizer illustrating the manner in which the overhanging rim covers the gap between the liner and the cheek plate; and 
         FIG. 14  is a partial cross sectional view of the liner installed in the grinding chamber as shown in  FIG. 13 , further illustrating the manner in which a liner constructed according to the present invention is installed in the grinding chamber of a coal pulverizer. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     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 rotary coal pulverizer 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 coal pulverizers, or other applications that do not involve coal as the raw material. In other words, the specific material and size reduction process is 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 grinding side chamber liner (hereinafter also referred to as a “liner”) 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 clip 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  consists essentially of 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 . Swing hammers  22  mounted on and driven by center shaft  20 , along with impact liners (not shown), operate to crush the coal against a grid (not shown). High temperature primary air is used to flash dry any surface moisture on the coal, which helps minimize the effect of moisture on coal capacity, coal fineness, and power consumption, among other things. 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 grinding and impeller clips  26  disposed on a rotating disc or wheel assembly  28  and stationary pegs  24  mounted on an opposing cheek plate  30  which abuts the interior grinding chamber wall  32 . The staggered arrangement of clips  26  extending from wheel assembly  28 , and pegs  24  extending from cheek plates  30 , form an interdigitated relationship in the interior of grinding section  16 . 
     Wheel  28  is mounted on and driven by center shaft  20 , preferably at a relatively high rate of speed. In operation, the movement of clips  26  and pegs  24  cause the turbulent flow of coal particles within the grinding section  16 . The turbulent flow and impact momentum on particles create a particle to particle attrition which further reduces the size of the coal particles received from crusher-dryer section  14 . The turbulent flow also results in punishing coal impact within interior grinding section  16  that could eventually damage grinding chamber wall  32 . 
     Cheek plates  30  and, up to now, liners  34  were used to protect the interior grinding chamber wall  32  in prior art devices. As shown particularly in  FIG. 4 , a prior art liner  34  includes a front surface  36  and opposing back surface  38 , upper end  40 , lower end  42 , inner edge  44  and outer edge  46 . As shown in  FIGS. 4 and 5 , two threaded holes  48  in front surface  36  extend through liner  34  for fastening liner  34  in grinding section  16  such that back surface  38  abuts the interior of grinding chamber wall  32 . Liner  34  is generally curved along its longitudinal axis between upper end  40  and lower end  42 , to match the curvature of cheek plates  30 , among other things. Outer edge  46  is longer than inner edge  44  due to the curved shape of liner  34 , which permits liner  34  to be disposed in a radially outer position with respect to cheek plates  30 . The thickness of liner  34  between front surface  36  and back surface  38  gradually decreases to inner edge  44 . The thickness begins to decrease at a brow  50 , which extends longitudinally along liner  34  between upper end  40  and lower end  42  and runs parallel to outer edge  46 , as illustrated by the arrow D 1 . 
     In contrast,  FIGS. 6-14  illustrate grinding chamber side liners constructed in accordance with the present invention. Liner  134  is generally curved longitudinally in the same fashion as liner  34 . In this embodiment, brow  150  extends from upper end  140  and lower end  142  toward inner edge  144 , converging at or about the longitudinal midpoint of inner edge  144 . The configuration of brow  150  forms two opposing inner corners  152   a  and  152   b  which decrease in thickness as they extend in the direction of inner edge  144  and towards upper and lower ends  140  and  142 , respectively, as illustrated by the arrow D 2 . The angle formed by D 2  can range from about 1 to about 50 degrees, and is preferably between 5 and 15 degrees. 
     Alternative configurations of side liners which include a reduction in thickness adjacent the radially inner edge are shown in  FIGS. 8-9  and  11 - 12 . Side liner  234  of  FIGS. 8 and 11 , includes a brow  250  that converges at or about the midpoint of inner edge  244  as in side liner  134 . However, brow  250  of side liner  234  begins at a location on upper and lower ends  240  and  242  that is radially inner when compared with the placement of brow  150  on side liner  134 . As shown in  FIGS. 9 and 12 , side liner  334  includes fastening holes  248  that are placed at a location which is radially inner when compared to the location of holes  148  in side liner  134 . 
     One of the main problems found with prior art liner  34  is the approximately ½ inch (about 12.7 mm) gap formed between inner edge  44  of liner  34  and the outer edge of cheek plate  30  when liner  34  is installed. This gap allows coal flow therein which impacts the housing wall, in particular, the lower housing division plate, causing damage thereto. The wear and tear eventually forces the entire system to be shut down for repairs. 
     In this embodiment, front surface  132  of liner  134  also extends beyond inner edge  144  to form an overhanging rim or ledge  154  and shoulder  156  underneath. Shoulder  156  allows the liner  134  to fit in the same location as prior art liner  34  while overhanging ledge  154  covers the gap between the inner edge  144  of liner  134  and the outer edge of cheek plate  30 . Thus, the configuration of liner  134  protects the housing wall, as shown in particular in  FIGS. 13 and 14 , among other things. A shim can be used between rear surface  138  and the housing wall to extend liner  134  from the wall so that overhanging ledge  154  fits properly over cheek plate  30 , if necessary, as shown by the arrow D 3 . 
     Liner  134  can be constructed of any materials capable of withstanding the punishing wear and tear of being used in a pulverizer, such as pulverizer  12 , such as Ni-Hard (i.e., cast iron to which nickel has been added to make it resist abrasion). 
     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 grinding chamber side liner 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.