Abstract:
The present application provides an attritor for reducing particles in size. The attritor may include a tank, one or more screens therein, a number of arms rotating therein, and a grinding media therein. The screens define a number of chambers therein such that the arms and the grinding media reduce the size of the particles in a first chamber to a first predetermined size and reduce the size of the particles in a second chamber to a second predetermined size.

Description:
TECHNICAL FIELD 
       [0001]    The present application and the resultant patent relate generally to mixers and grinders for use with a flow of a coal slurry and the like and more particularly relate to a continuous flow attritor producing a substantially uniform particle size distribution therein. 
       BACKGROUND OF THE INVENTION 
       [0002]    Syngas may be produced by using a gasification process in which a carbonaceous fuel source such as coal reacts with oxygen within a gasifier. The carbonaceous fuel source may include a coal slurry in which coal particles are dispersed within a liquid. The coal particles should be reduced to a substantially uniform predetermined size before the reaction. One common type of a grinding or a dispersing device for coal is an attritor. The coal slurry may be premixed with a grinding media and pumped into an attrition vessel. The coal slurry and the grinding media are then agitated within the tank by a rotating shaft with a number of arms. This action causes the grinding media (spherical steal bearing balls) to exert shearing and impact forces on the particles in the coal slurry so as to reduce the size of the particles before use in the gasifier and/or other processing. 
         [0003]    Current attritor designs, however, may require the use of an oversized injection pump given the use of the inlet port at the bottom of the tank. The injection pump needs to overcome not only the pipe and pipe accessories at the inlet but also the hydrostatic pressure of the column therein. Injecting the coal slurry at the bottom of the tank and removing the coal slurry at the top of the tank may create concentration surges developing along the height of the tank. These concentration surges may be defined by concentration profiles or non-uniform particle sizes that may be denser at the bottom and lighter on the top. Given such, the flow at the inlet port and at the discharge port of a conventional attritor may not have the same solids or particle size distribution therein such that the flow therethrough cannot be steady state or continuous in mass and concentration. 
         [0004]    There is thus a desire for an improved attritor and methods of use thereof. Preferably such an improved attritor may provide substantially steady state, continuous flow with a substantially uniform particle size distribution therein. Moreover, the effective costs of operation also may be reduced herein by reducing the size or capacity of the injection pump and the like. 
       SUMMARY OF THE INVENTION 
       [0005]    The present application and the resultant patent provide an attritor for reducing particles in size. The attritor may include a tank, one or more screens therein, a number of arms rotating therein, and a grinding media therein. The screens define a number of chambers therein such that the arms and the grinding media reduce the size of the particles in a first chamber to a first predetermined size and reduce the size of the particles in a second chamber to a second predetermined size. 
         [0006]    The present application and the resultant patent further provide a method of reducing particles in size in an attritor. The method may include the steps of pumping the particles to a top of the attritor, agitating the particles in a first chamber to a first predetermined size, dropping the particles into a second chamber, agitating the particles in the second chamber to a second predetermined size, and discharging the particles at a bottom of the attritor. 
         [0007]    The present application and the resultant patent further provide for an attritor for reducing coal particles in size. The attritor may include a tank, a first screen defining an upper chamber, a second screen defining a lower chamber, a number of arms rotating therein, and a grinding media therein. The arms and the grinding media reduce the size of the coal particles in the upper chamber to a first predetermined size and further reduce the size of the coal particles in the lower chamber to a second predetermined size therein. 
         [0008]    These and other features and improvements of the present application and the resultant patent should become apparent to one of ordinary skill in the art upon review of the following detailed description when taken in conjunction with the several drawings and the appended claims. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0009]      FIG. 1  is a schematic diagram of an attritor and related components as may be described herein. 
           [0010]      FIG. 2  is a schematic diagram of the interaction of coal slurry and a grinding media for use in the attritor of  FIG. 1 . 
       
    
    
     DETAILED DESCRIPTION 
       [0011]    Referring now to the drawings, in which like numerals refer to like elements throughout the several views,  FIG. 1  shows an example of an attritor  100  as may be described herein. The attritor  100  may include a tank  110 . The tank  110  may be any type of vertical vessel. The tank  110  may be substantially hollow. The tank  110  may be made out of a substantially abrasion resistant steel or similar type of materials. The tank  110  may have a lining therein to protect further against abrasion, erosion, corrosion, and the like. In this example, the tank  110  may have a height of about 100 inches (about 254 centimeters) and a diameter of about 36 inches (about 93 centimeters) or so. The tank  110 , however, may have any suitable size, shape, or configuration to meet a specific capacity. 
         [0012]    The tank  110  may have an inlet port  120  positioned about a top end  130  thereof. The tank  110  also may have a discharge port  140  about a bottom end  150  thereof. The inlet port  120  and the discharge port  140  may have any suitable size, shape, or configuration. Multiple inlet ports  120  and/or discharge ports  140  also may be used herein. One or more slurry pumps  160  and the like may be in communication with the inlet pump  120 . The slurry pump  160  may be of conventional design and may have any suitable size or capacity. The tank  110  also may have a number of manholes positioned thereon. In this example, a first manhole  170  and a second manhole  180  are shown. Any number of the manholes may be used herein. The manholes  170 ,  180  may have any suitable size, shape, or configuration. Other components and other configurations may be used herein. 
         [0013]    The attritor  100  may include a rotating shaft  190  with a number of arms  200  positioned within the tank  110 . The rotating shaft  190  may extend about the length of the tank  110  while the arms  200  may extend within the width thereof Any number of the arms  200  may be used in any suitable size, shape, or configuration. The arms  200  may have uniform or differing shapes. The rotating shaft  190  and the arms  200  may be made out of any type of substantially abrasion resistant material. As is shown, the arms  200  may have a somewhat staggered positioning along the length of the rotating shaft  190 . Other positions may be used herein. 
         [0014]    The rotating shaft  190  may be suspended at the top  130  of the tank  110  by a thrust-radial roller bearing  210  and the like. The roller bearing  210  may be of conventional design and may have any suitable size, shape, or configuration. The roller bearing  210  may be removable such that the rotating shaft  190  may be replaced via the top  130  of the tank  110 . The rotating shaft  190  may be connected to a gear reducer  220  and a motor  230 . The gear reducer  220  and the motor  230  may be of conventional design and may have any suitable size, shape, configuration, or capacity. The motor  230  may be a conventional electric motor. The gear reducer  220  may bring the nominal speed of the motor  230  from about 1800 revolutions per minute to about 90 revolutions per minute. Other speeds and speed ratios may be used herein. Other type of drive means and gearing means may be used herein. 
         [0015]    The attritor  100  also may include a number of mesh screens  240  positioned within the tank  110 . In this example, a first screen  240  and a second screen  250  are shown. Any number of screens may be used herein. The first screen  240  may have a mesh of about 700 micrometers or may be in a range from about 600 to about 1200 micrometers or so. The second screen  250  may have a mesh of about 350 micrometers or may be in a range from of about 20 to about 590 micrometers. The screens may be made out of any type of substantially abrasion resistant material. Other sizes, shapes, and configurations may be used herein. The screens  240 ,  250  may divide the tank  110  into an upper chamber  260  and a lower chamber  270 . The chambers may have the same or differing volumes. Any number of the chambers may be used herein. Other components and other configurations may be used herein. 
         [0016]    As is shown in  FIG. 2 , the attritor  100  may be used to grind sequentially a number of particles  280  from a first larger size to a second smaller size. In this example, the particles  280  may be coal particles  290  suspended in a slurry  300 . Other types of particles  280  may be used herein. The grinding process may involve the interaction of the particles  280  with a grinding media  310 . In this example, the grinding media  310  may be in the form of a number of chrome steel balls  320 . Other types of grinding media  310  and other types of materials may be used herein. The grinding media  310  may have differing sizes. In this example, an upper grinding media  330  in the upper chamber  260  may have a diameter of about 0.5 inches or so (about 1.27 centimeters) while a lower grinding media  350  in the lower chamber  270  may have a diameter of about a 0.25 inches or so (about 0.635 centimeters). Other suitable sizes, shapes, or configurations may be used herein. 
         [0017]    In use, about two-thirds or so of the upper chamber  260  and the lower chamber  270  may be filled with the grinding media  310 . Other volumes may be used herein. The coal slurry  300  may be pumped to the top  130  of the tank  110  into the inlet port  120 . The coal slurry  300  thus settles into the tank  130  under the force of gravity. Upon entry, the coal particles  290  may have an average diameter of about 2 millimeters. The grinding media  310  may be forced into motion via rotation of the arms  200  by the rotating shaft  190 , the roller bearing  210 , the gear reducer  220 , and the motor  230 . The rotation of the arms  200  moves the grinding media  310  and creates a violent interaction with the coal particles  290 . This agitating interaction of media to coal, coal to coal, and coal to wall (of the tank) thus reduces the size of the coal slurry particles in a substantially uniform fashion. 
         [0018]    Once the coal particles  290  have been reduced to about 300 micrometers in diameter in the upper chamber  260 , the particles  290  are appropriately sized to pass through the mesh of the first screen  240  and fall into the lower chamber  270  under the force of gravity. The smaller lower grinding media  340  used in the lower chamber  270  continues the reduction in the size of the coal particles  290 . The coal particles  290  thus may be reduced from about 300 micrometers to about 15 to about 20 micrometers or so. At this size, the coal particles  290  may fall through the mesh of the second screen  250  and into the discharge port  140  under the force of gravity. The grinding in the lower chamber  270  also may be assisted by upper grinding media  330  from the upper chamber  260  that may have degraded and fallen into the lower chamber  270 . This degraded media will continue interaction with the coal particles  290  and assist in a further size reduction therein. The coal particles  290  thus may have a uniform particle size distribution upon leaving the discharge port  140 . The grinding media  310  may be removed from the coal slurry  300  via magnetic means, a settlement tank, and the like. Other types of separation means may be used herein. 
         [0019]    Given the use of the inlet port  120  at the top end  130  of the tank  110 , the slurry pump  160  of the attritor  100  need only be sized to pump the coal slurry  300  from ground level to the inlet port  120  instead of all of the way through the tank  110  from the bottom end  150  thereof. Moreover, the degradation of the grinding media  310  may be slower given the use of the upper chamber  260  and the lower chamber  270  in that the grinding media  310  from the upper chamber  260  will continue to work in the lower chamber  270 . 
         [0020]    Given the use of the two sequential chambers  260 ,  270  with each chamber dedicated to a specific particle size distribution, the attritor  100  largely mimics the operation of a steady state, continuous flow device even if each chamber in fact acts on a batch basis. Specifically, the attritor  100  may avoid the concentration surges that create concentration profiles along the height of the tank  130  as may be found in known devices given the use of the multiple chambers. Any number of the chambers may be used herein with more chambers possibly more closely approximating an actual continuous, steady state flow in mass and concentration. Each chamber further reduces the particle size in sequence. 
         [0021]    It should be apparent that the foregoing relates only to certain embodiments of the present application and the resultant patent. Numerous changes and modifications may be made herein by one of ordinary skill in the art without departing from the general spirit and scope of the invention as defined by the following claims and the equivalents thereof.