Abstract:
A coal processing mill incorporates integral systems for coarse coal dewatering, grinding, injection of a peptizing agent into the ground coal stream before it enters an agitation zone (where the peptization process takes place), passing the treated coal and the peptized clay and ash through a separating valve and passing the separated coal on to final drying. In other embodiments, ash and pyrites (of much higher density than coal) are separated from coal and the coal can then be fired.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     The present patent application is based on, and claims priority from, U.S. provisional Application No. 60/107,666, filed Nov. 9, 1998, which is incorporated herein by reference in its entirety. 
    
    
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to mills for grinding and separating ash and pyrites from coal. More specifically, the invention relates to such mills, which incorporate systems for cleaning and drying coal as well as grinding it. 
     2. Related Art 
     In preparing coal for briquetting or pelletizing, ash materials and moisture interfere with successful bonding of finely ground particles into a cohesive mass that will maintain its integrity with storage and handling. 
     Clay in the ash attracts and holds water. It generally helps maintain a water content of around 30% by weight. This is undesirable because it lowers the Btu value, resulting in increased shipping costs and less boiler efficiency. 
     In prior art coal processing technology, coarse dewatering takes place at one site. The coarsely dewatered coal is then transported to a grinding site, thence to a peptizing tank, then on to a dewatering screen process or centrifugal operation, followed by aeration to achieve sufficient dryness for maximum bonding results. No ash removal takes place in such prior art technology, unless it is done by wet methods as a separate step. 
     In addition, in some parts of the wold, coal has extremely high ash content, as much as 35 percent. Currently, conventional milling is done at high maintenance expense to both mills and boilers. Boilers in particular require costly de-slagging to remove encrustations from molten ash. Milling followed immediately, in the same rotating device, by ash separation provides a compact, integrated unit for replacing existing conventional mills as a way to substantially reduce the costs of combusting high-ash coals. 
     SUMMARY OF THE INVENTION 
     The objects of this invention are several: to dewater incoming wet coal; to fine-grind the coal; to remove minerals and clay components of ash so that the powdered coal can be more thoroughly dried by centrifugal means, down to around 5% by weight, and thus more amenable to briquetting or pelletizing; or to remove ash from coal prior to direct firing. 
     Experience has shown that by peptizing the clay into a colloidal dispersion by washing the coal particles with vigorous agitation in a soap-like agent, such as sodium hexametaphosphate, the fine platelets of clay can be removed from the small coal particle surfaces making them hydrophobic, thus making it easier to remove the clinging water. The colloidal mix of clay can then be centrifugally separated from the coal. The insoluble mineral portion of the ash can also be centrifuged from the coal. After the peptized clay and mineral containing ash is split off and ejected the clean but still damp coal continues on through an intensive centrifugal drying action. 
     All of these functions—coarse coal dewatering, grinding between high speed counter rotating rotors, injection of the peptizing agent into the ground coal stream before it enters the violent agitation zone (where the peptization process takes place), having the treated coal pass through the peptized clay and ash removal point and then on to the final drying phase for the coal—are performed by respective means that are all incorporated into one integral milling unit. 
     The processor technology preparing coal for pelletizing in accordance with the present invention is not only superior because of what it does and how it does it, but also because of its relative simplicity. There is no coarse dewatering at one site, transporting to a grinding site, thence to a peptizing tank, then on to a dewatering screen process or centrifugal operation, followed by aeration to achieve sufficient dryness for maximum bonding results. The present invention also accomplishes ash removal, which is not achieved in the prior art technology. 
     Similarly, in preparing high ash coal for direct firing, there is no present technology that performs efficient, high-capacity, ultra-fine milling to liberate high proportions of ash from coal followed immediately by dry separation, nor efficient, stand-alone, high capacity, dry ash separation means. 
     Other objects, features and advantages of the present invention will be apparent to those skilled in the art upon a reading of this specification including the accompanying drawings. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The invention is better understood by reading the following Detailed Description of the Preferred Embodiments with reference to the accompanying drawing figures, in which like reference numerals refer to like elements throughout, and in which: 
     FIG. 1 is a transverse cross-sectional view of a coal mill incorporating a coal grinding, cleaning, and drying processor in accordance with the present invention. 
     FIG. 2 is a cross-sectional view of the processing rotors of the coal grinding, cleaning, and drying processor in accordance with the present invention. 
     FIG. 3 is an enlarged view of the cleaning (separating) and drying zones of the processing rotors of FIG.  2 . 
     FIG. 4 is a cross-sectional view of the cleaning zone (separator) of a second embodiment of the invention for removing ash and pyrites from coal in preparation for direct boiler firing. 
     FIG. 5 is a cross-sectional view of the separator of a third embodiment for removing ash and pyrites from coal, in which the higher density constituent moves in the same general direction (upward) as the material feeding into the separator. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     In describing preferred embodiments of the present invention illustrated in the drawings, specific terminology is employed for the sake of clarity. However, the invention is not intended to be limited to the specific terminology so selected, and it is to be understood that each specific element includes all technical equivalents that operate in a similar manner to accomplish a similar purpose. 
     Referring now to FIG. 1, there is shown a mill of general form including drives and rotors into which the present invention is incorporated. The drives and rotors may be of the type disclosed in co-pending U.S. patent application Ser. No. 09/302,359, filed Apr. 30, 1999, of Charles Kepler Brown. Jr. (the inventor of the present application) and David Kepler Brown, and U.S. Pat. No. 5,275,631 to the same inventors, which are incorporated herein by reference in its entirety; while the mill itself may be of the type disclosed in co-pending international application No. PCT/US99/19504, filed Aug. 26, 1999, of the same inventors, which is also incorporated herein by reference in its entirety. 
     FIG. 2 shows a cross section of the processing rotors R involved in the previously described actions. The rotors R are driven by motors in clockwise and counter-clockwise relation with each other. All of these means are housed in a single and appropriate housing. 
     Incoming coal, which in the first embodiment typically might be drawn from a storage pond of waste coal, is fed into the mill M through a feed pipe  1  positioned at the top of the mill M along the axis of rotation of the rotors R. The coal is deposited in a dewatering bowl  2  positioned below and spaced downwardly from the outlet of the feed pipe  1 . A cup  3  is provided surrounding the lower portion of the feed pipe  1 , the bottom of the cup  3  being co-terminous with the outlet of the feed pipe  1 . Both the bowl  2  and the cup  3  are of approximately frusto-conical shape. The cup  3  is connected to the bowl  2  by means of connecting bars  3   a.    
     The exterior surface of the cup  3  is spaced inwardly from the interior surface of the bowl  2  to define an approximately frusto-conical space  5 , including a zone  5   a  between the outer bottom of the cup  3  and the inner bottom of the bowl  2 . The cup  3  directs process material radially outward toward the inner wall of the bowl  2  under centrifugal force, and then forms a relatively thin (for quick drainage) shell-like layer  4  of wet coal in the space  5 . 
     The centrifugal force developed by the mass at the bottom of the cup  3  in the zone  5   a  exerts pressure on the bottom of the shell  4 , urging it upward as fast as the incoming coal will displace it. The angle of the external slope of the cup  3  can be set to provide an upward force component just low enough that the coal would not move except for the centrifugal force generated in the zone  5   a.  As long as the incoming coal continues the flow through, milling will continue. 
     The interior side wall of the bowl  2  is provided with an annular groove  6  and a plurality of radial ports  7  formned through the side wall at the upper edge of the annular groove  6 . The upwardly migrating coal passes over the annular groove  6  in the bowl  2 , while the centrifuged water traveling up the inner surface collects in the annular groove  6  and ejects through the ports  7 . The dewatered coal continues on up and over a rim  8  formed at the upper peripheral edge of the bowl  3  and enters the grinding section  9  between the rotors R. 
     Several styles of rotor configuration for grinding can be utilized here based on a variety of coal characteristics. One such style is shown in U.S. Pat. No. 5,275,631; others are shown in co-pending U.S. patent application Ser. No. 09/302,359. 
     As the ground coal sprays out from between the lips  10  formed at the perimeters of the rotors R, it enters a peptizing zone defined between opposed, counter-rotating upper and lower agitating rings  14  and  15  concentric with the rotors R and abutting the lips of the rotors R. Rings  14  and  15  have approximately the form of truncated cones. 
     The coal is saturated with an incoming stream of peptizing agent by way of a nozzle  11  spraying into an annular groove or cavity  12  in the upper ring  14  and draining into the space between the rings  14  and  15  through a plurality of port holes  13  (shown in FIG. 3) formed in and spaced appropriately around the groove  12 . Centrifugal force is the pumping agent. The peptizing agent can alternatively be injected in similar manner further back in the rotor system. 
     The saturated mix is driven centrifugally out and up between the rings  14  and  15 . Various rippled or ridged patterns  16  can be incorporated into the facing surfaces of the rings  14  and  15  to provide an extremely vigorous scrubbing action on the saturated coal layer. 
     An annular collar enclosing the upper edge of the lower ring  15  defines a manometer-like valve  17  having a looped fluid path and an exit leg  19  therethrough. The surface of the collar at the inlet of the valve  17  defines a weir-like barrier  18  opposite the upper edge of the upper ring. 
     By the time the fluidized, peptized well-scrubbed mass reaches the branch  30  (shown in FIG. 3) between the barrier  18  and the valve  17 , the dense ash particles are firmly following the surface of the ring  15  and displacing the less dense clean coal to an upper stratum. Close to 2000 g&#39;s of centrifugal force, the fluid nature of the mix, and the density difference of coal and ash ensure that stratification preceding separation will occur. At branch  30 , the peptized, clay-carrying fluid ejects through the manometer-like valve  17 , while the layer of insoluble, more dense mineral ash particles bank up against the barrier  18 . The unbalanced forces resulting from the bank-up move the ash material out through the loop and exit leg  19  of the valve  17 . Liquid from a nozzle  35 , injected into the loop of the valve  17 , maintains free movement of solids through the loop. Water is presently considered to be the preferred liquid, although other liquids can be used. While this action relieves the rings  14  and  15  of the ash, it also blocks the flow of pure, less dense coal and forces it to flow up and over the barrier  18 . 
     It is possible that materials other than coal, comprising constituents of differing densities, could be processed in this way. The zone between the facing surfaces of the rings  14  and  15  is formed on an angle of between 45 and 85 degrees, depending on the size distribution of the material being processed, the amount of liquid present, and the rotation rate, all of which may vary with the feed stock and the purpose for processing. For coal, currently, an optimum angle is thought to be between 45 and 85 degrees, and most likely within 50 to 65 degrees. 
     The damp, cleaned coal is further dried in a drying zone  31  upstream of the peptizing zone. The drying zone is defined by a cup  24  extending upwardly from the collar defining the valve  17 . The cup  24  has approximately the form of a truncated cone, with its interior sidewall forming an angle of about 50 to 70 degrees with a horizontal plane. It is configured in a manner similar to the dewatering bowl  2 , in that the interior side wall of the cup  24  is provided with an annular groove  20  and a plurality of radial ports  21  formed through the side wall at the upper edge of the annular groove  20 . In the cup  24 , water collects in the annular groove  20 , and drains out through the ports  21 . The clean, dry coal extrudes up over the rim  23  of the cup  24 . A cover section  25  having approximately the form of a truncated cone is provided over the cup  24 , and entrains the coal movement so it does not blow away before it is dried. The cover  25  is mounted on the cup  24  and travels with it. 
     The wastewater and ash collect in an annular channel  26  positioned radially outwardly of the rotors R and below the outlets of the ports  21 , and is drained or flushed to a waste pond. The coal goes on to be briquetted or pelletized. 
     FIG. 4 illustrates an embodiment in which grinding is followed by separation, without peptizing. This embodiment is preferred when the coal product is not to be pelletized or briquetted, but instead is to be fired directly after cleaning. In this embodiment, a ring  41  is concentric with and abuts the lip of the lower rotor R. An annular shield  40  and a valve  42  are connected by radial ties (not shown) to the ring  41 . The surface  43  if the valve  42  immediately above the inlet of the valve  42  acts as a weir similar to the barrier  18  described in connection with FIGS. 2 and 3. It will be appreciated that the facing surfaces of the shield  40  and the ring  41  are smooth, rather than patterned as in the case of the facing surfaces of the rings  14  and  15  of the first embodiment. A nozzle  35  is provided, similar to the nozzle  35  described in connection with FIGS. 2 and 3. 
     By the time the moving mass of coal and ash particles reaches the branch  44  between the weir  43  and the valve  42 , the dense ash particles are firmly following the surface of the ring  41  and displacing the less dense clean coal to an upper stratum. At the branch  45 , the coal passes over the weir  43  (no peptizing having taken place), while the more dense mineral ash particles bank up against the weir  43 . The unbalanced forces resulting from the bank-up move the ash material out through the loop  42   a  and the exit leg of the valve  42 . The curve of the loop  42   a  of through the valve  42  is in the same direction as the flow of less dense particles. Liquid from the nozzle  35 , injected into the loop  42   a,  maintains free movement of solids through the loop. 
     Referring now to FIG. 5, there is shown a third embodiment also for use where the coal product is not to be pelletized, and where grinding therefore is followed by separation, without peptizing. In this embodiment, a rotor ring  51  is provided concentric with and abuts the lip of the lower rotor R. The rotor ring  51  is integrated with the loop  50   a  of the separator valve  50 , and waste material is directed along an upward path instead of downwardly. In this case, the curve of the loop  50   a  through the valve  50  is in the opposite direction from the flow of less dense particles. Less dense coal travels over a weir ring  52  provided over the upper edge of the rotor ring  51 . An annular shield  53  and the weir ring  52  are connected by radial ties (not shown) to the ring  51 . 
     Modifications and variations of the above-described embodiments of the present invention are possible., as appreciated by those skilled in the art in light of the above teachings. It is therefore to be understood that, within the scope of the appended claims and their equivalents, the invention may be practiced otherwise than as specifically described.