Abstract:
In a coal preparation plant which receives a raw coal feed and separates the raw coal feed into clean coal feed and refuse feed slurries using a media based separation process, an apparatus is provided for use therein. The inventive apparatus simultaneously processes the raw coal feed and clean coal feed and refuse feed slurries, while occupying minimal floor space within the coal preparation plant. The inventive apparatus includes a unitary vibrating screen assembly having a length and a width, wherein the width of the vibrating screen assembly is partitioned into three screen sections extending the length of the vibrating screen assembly. A deslime screen section receives the raw coal feed and separates the raw coal feed into coarse and fine sized fractions as the raw coal feed moves along the length of the deslime screen section. A refuse screen section receives the refuse feed slurry and removes separation media therefrom as the refuse feed slurry moves along the length of the refuse screen section. Similarly, a clean coal screen section receives the clean coal feed slurry and removes separation media therefrom as the clean coal feed slurry moves along the length of the clean coal screen section.

Description:
FIELD OF THE INVENTION  
         [0001]    The present invention is directed generally toward coal preparation plants and, more particularly, toward an improved screen assembly apparatus for use in coal preparation plants.  
         BACKGROUND OF THE INVENTION  
         [0002]    Coal preparation plants separate organic and non-organic solid particles by their specific gravities. The coal preparation plant receives a feed of raw mined coal, and separates the raw mined coal into clean coal and refuse. These plants typically utilize two basic processing methods for separating raw coal from rock and varying proportions of striated rock and coal from the higher quality coal. The two processing methods include heavy media and water based separation methods. Heavy media, utilizing a slurry of media, e.g., water and magnetite or ferrosilicon, to separate the coal from the refuse according to their specific gravity of dry solids, is the most common separation process for larger size (Plus 1 mm-0.5 mm) particles. Whereas, water based separation processes are more commonly used for the “cleaning” of the finer sized particles, as that term is conventionally understood in the coal processing art. One type of heavy media circuitry used in the coal preparation plants includes a heavy media cyclone.  
           [0003]    Coal preparation plants using heavy media cyclones operate with three separate types of screens for coal processing, namely, a deslime screen, a refuse screen and a clean coal screen. A common screening assembly used in many coal preparation plants is today known as a vibratory banana screen. The deslime screen receives the raw coal feed particles and separates them into coarse and fine sized fractions. The coarse or larger sized particles discharged from the screen surface are directed to the heavy media separation section of the coal preparation plant, while the finer sized particles passing through the deslime screen are directed toward the water based separation section of the coal preparation plant.  
           [0004]    The separate clean coal and refuse screens receive the clean coal and refuse particles, respectively produced by the heavy media separating section. While on the clean coal and refuse screens, the clean coal and refuse particles are rinsed with water, and the finer particles and water passing through the respective screens are recirculated through the coal preparation plant. Rinsing the clean coal and refuse particles is primarily done to recover the particles of media, such as magnetite, remaining thereon as a result of the coal/refuse separation process, as magnetite can be quite expensive.  
           [0005]    Often, the deslime, clean coal and refuse screens are located in different areas of the coal preparation plant and/or on different floors. In addition to being an inefficient use of space and increasing the cost of the coal preparation plant, this situation creates a burden for the plant operator wishing to view the feeds and discharges of raw coal, clean coal and refuse screens.  
           [0006]    The present invention is directed toward overcoming one or more of the above-mentioned problems.  
         SUMMARY OF THE INVENTION  
         [0007]    In a coal preparation plant which receives a raw coal feed and separates the raw coal feed into clean coal and refuse particles using a media based separation process, an apparatus is provided for use therein. The inventive apparatus simultaneously processes the raw coal feed, clean coal and refuse particles, while occupying minimal floor space within the coal preparation plant. The inventive apparatus includes a unitary vibrating screen assembly having a length and a width, wherein the width of the vibrating screen assembly is partitioned into three screen sections extending the length of the vibrating screen assembly. A deslime screen section receives the raw coal feed particles and separates the raw coal feed particles into coarse and fine sized fractions as the raw coal feed particles move along the length of the deslime screen section. Two separate drain and rinse sections of the screen receive the refuse and clean coal particles, respectively, and remove media remaining on these particles as they move along the length of the respective screen section.  
           [0008]    Typically, the various feed particles are moved along the length of the unitary vibrating screen assembly via gravitational and/or vibrating forces. The unitary vibrating screen assembly may be of single or double deck construction, as those terms are conventionally understood in the coal processing art.  
           [0009]    In one form, the deslime screen section includes an underpan receiving the fine sized raw coal feed particles passing through the deslime screen section. The fine sized raw coal feed particles received by this underpan are passed to a fine coal, or water based, processing section of the coal preparation plant. The two separate drain and rinse sections each include a separate underpan receiving the media particles which pass through the respective screen section and are recovered from the refuse and clean coal particles. The recovered media particles received by these underpans are recirculated through and/or further processed by the coal preparation plant.  
           [0010]    The underpans of the two separate drain and rinse sections may be combined into a single underpan receiving the recovered media particles passing through the screen sections, respectively, for recirculation through and/or further processing by the coal preparation plant.  
           [0011]    Sprayers are provided for adding water onto the deslime screen section, and the two separate drain and rinse screen sections to rinse the raw coal feed, refuse and clean coal particles, respectively. Water is used to aid in particle separation in the deslime screen section and also to remove media from the refuse and clean coal particles in the two drain and rinse screen sections, respectively.  
           [0012]    In another form, partition members are provided lengthwise along the unitary vibrating screen assembly extending vertically therefrom to partition the unitary vibrating screen assembly into the deslime and the two separate drain and rinse screen sections.  
           [0013]    In a preferred form, the inventive unitary vibrating screen assembly includes a multislope “banana” screen of either a single or double deck configuration.  
           [0014]    It is an object of the present invention to:  
           [0015]    provide an improved screen assembly in a coal preparation plant occupying minimal space; and  
           [0016]    to provide an improved screen assembly for simultaneously processing raw coal feed, refuse feed and clean coal feed particles.  
           [0017]    Other objects, aspects and advantages of the present invention can be obtained from a study of the specification, the drawings, and the appended claims. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0018]    [0018]FIG. 1 is a perspective view of a screen assembly according to the present invention;  
         [0019]    [0019]FIG. 2 is a block diagram of a coal preparation plant incorporating the inventive screen assembly;  
         [0020]    [0020]FIG. 3 is an exploded perspective view of the inventive screen assembly with partition members removed;  
         [0021]    [0021]FIG. 4 is a side view a raw coal deslime section of the inventive screen assembly;  
         [0022]    [0022]FIG. 5 is a side view of a refuse section of the inventive screen assembly; and  
         [0023]    [0023]FIG. 6 is a side view of a clean coal section of the inventive screen assembly. 
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0024]    Referring to FIGS.  1 - 2 , the inventive screen assembly  10  is shown incorporated for use within a coal preparation plant  12 . The coal preparation plant  12  typically receives a raw coal feed  14  and separates the raw coal feed  14  into clean coal  16  and refuse  18  particles. The inventive screen assembly  10  includes a unitary screen assembly for simultaneously processing the raw coal feed  14 , clean coal  16  and refuse  18  particles. The screen assembly  10  has a length “l” and a width “w” and is partitioned into deslime  20 , refuse  22  and clean coal  24  screen sections extending lengthwise, with each section receiving and processing a different type of feed particle.  
         [0025]    The deslime screen section  20  includes top  26  and bottom  28  deck screens. The top screen  26  includes a mesh which is larger than the mesh of the bottom screen  28 . The bottom screen  28  is disposed directly below the top screen  26 , and as the raw coal feed  14  is passed across the length of the deslime screen section  20 , the top  26  and bottom  28  screens screen the coarse raw coal feed particles from the finer sized particles which fall through the screens  26  and  28  and into an underpan  30  disposed below the top  26  and bottom  28  screens. As a result of the larger mesh of the top screen  26 , the coarse raw coal feed particles  14  screened by the top screen  26  are of a larger diameter than those screened by the bottom screen  28 .  
         [0026]    The refuse screen section  22  also includes top  32  and bottom  34  deck screens, with the bottom screen  34  disposed below the top screen  32 . The top screen  32  has a mesh which is larger than the mesh of the bottom screen  34 . As the refuse particles  18  are passed across the length of the refuse screen section  22 , the solid refuse particles are screened by the top  32  and bottom  34  screens, with the finer sized particles of refuse (misplaced refuse fines) passing through the screens  32  and  34  to an underpan  36  disposed below the top  32  and bottom  34  screens. As a result of the larger mesh of the top screen  32 , the solid refuse particles  18  screened by the top screen  32  are of a larger diameter than those screened by the bottom screen  34 .  
         [0027]    Similarly, the clean coal screen section  24  includes top  38  and bottom  40  deck screens, with the bottom screen  40  disposed below the top screen  38 . The top screen  38  has a mesh which is larger than the mesh of the bottom screen  40 . As the clean coal particles  16  are passed across the length of the clean coal screen section  24 , the solid clean coal particles are screened by the top  38  and bottom  40  screens, with the finer sized clean coal particles (misplaced clean coal fines) passing through the screens  38  and  40  and into an underpan  42  disposed below the top  38  and bottom  40  screens. As a result of the larger mesh of the top screen  38 , the solid clean coal feed particles  16  screened by the top screen  38  are of a larger diameter than those screened by the bottom screen  40 .  
         [0028]    As shown in FIG. 1, each of the screens  26 ,  28 ,  32 ,  34 ,  38  and  40  are sloped such that the inventive screen assembly type is of the type conventionally known as a banana screen. The top screens  26 ,  32  and  38  together constitute a first screen deck, while the bottom screens  28 ,  34  and  40  together constitute a second screen deck.  
         [0029]    A first partition member  44  separates the deslime  20  and refuse  22  screen sections. Similarly, a second partition member  46  separates the refuse  22  and clean coal  24  screen sections. The first  44  and second  46  partition members extend vertically from, and substantially normal to, the top screens  26 ,  32  and  38 . Similarly, third  48  and fourth  50  partition members extend vertically from the bottom screens  28 ,  34  and  40  up to the top screens  26 ,  32  and  38  and partition the bottom screens  28 ,  34  and  40  into the deslime  20 , refuse  22  and clean coal  24  screen sections, respectively. Specifically, the third partition member  48  separates the deslime screen section  20  from the refuse screen section  22 , while the fourth partition member  50  separates the refuse screen section  22  from the clean coal screen section  24 . Typically, the partition members  44 ,  46 ,  48  and  50  will be bolted to the frame (not shown) of the screen assembly  10 .  
         [0030]    As shown in FIG. 2, the feed particles  14 ,  16  and  18  are provided at a first, or input, end  51  of the screen assembly  10 , which is elevationally higher than a second, or output, end  52  of the screen assembly  10 . The feed particles  14 ,  16  and  18  are moved along the length of the screen assembly  10  via gravitational forces acting thereon. To aid in particle separation through the screens, and also to help move the particles along the screens, the screens of the screen assembly  10  are conventionally vibrated using a standard vibration device  53  (see FIGS.  4 - 6 ).  
         [0031]    As shown in FIG. 2, the coarse raw coal feed particles  14  screened by the top  26  and bottom  28  screens are fed to a first processing section  54  of the coal preparation plant  12 . The processing section  54  utilizes conventional coal processing techniques to develop the clean coal  16  and the refuse  18  particles. Typically, these techniques will include heavy media separation methods. The finer sized raw coal feed particles  14  falling to the underpan  30  are fed to a second processing section  55  which conventionally processes those finer sized coal particles, typically using water based separation methods.  
         [0032]    The solid refuse particles  18  screened by the top  32  and bottom  34  screens are fed to a conventional refuse handling section  56  of the coal preparation plant  12 . Similarly, the solid clean coal particles  16  screened by the top  38  and bottom  40  screens are fed to a conventional coal clean handling section  58  of the coal preparation plant  12 . Each of the finer sized refuse particles  18  and the finer sized clean coal particles  16  which are received in the underpans  36  and  42 , respectively, are fed to both the first processing section  54  and the second processing section  55  for recirculation through and/or further processing by the coal preparation plant  12 .  
         [0033]    As shown in FIGS.  3 - 6 , each of the screen sections  20 ,  22  and  24  includes sprayers  60  connected by valves  62  to a water source  64 . As the respective feed particles  14 ,  16  and  18  move along the lengths of the respective screen sections  20 ,  22  and  24 , they are sprayed with water. With regard to the deslime screen section  20 , water is typically applied on the raw coal feed  14  to aid in separating the finer sized raw coal particles from the coarse raw coal particles. The water and finer sized raw feed particles which pass through the top  26  and bottom  28  screens and into the underpan  30  are fed to the second processing section  55  via conduit  66  The coarse raw coal feed particles screened by the top  26  and bottom  28  screens are fed to the first processing section  54  via conduit  68 .  
         [0034]    With respect to the refuse  22  and clean coal  24  screen sections, rinsing the particles with water is done for a different reason. Typically, magnetite is used as the media by the first processing section  54  for separating the clean coal from the refuse. The first processing section  54  produces the clean coal  16  and refuse  18  particles as slurries of solid clean coal/refuse, misplaced clean coal/refuse fines, magnetite and water. Rinsing the solid refuse and clean coal particles passing across the refuse  22  and clean coal  24  screen sections, respectively, is done primarily to recover the magnetite particles for recirculation through and/or further processing by the coal preparation plant  12 .  
         [0035]    The underpan  36  of the refuse screen section  22  is divided into a drain section  66  generally nearer the input end  51  and a rinse section  68  extending from the drain section  66  to the output end  52 . Since the refuse feed  18  is received at the refuse screen section as a slurry of solid refuse, misplaced refuse fines, magnetite and water, the majority of the magnetite will be recovered from the refuse feed  18  in the drain section  66  of the underpan  36 , as it will simply pass through the screens  32  and  34 . However, the solid refuse particles screened by the screens  32  and  34  will have particles of magnetite adhering thereon. To recover this magnetite, the sprayers  60  are positioned to apply water to the screened solid refuse particles at the rinse section  68  of the underpan  36 . The magnetite and misplaced refuse fines rinsed off of the screened refuse particles by the sprayers  60  are received in the rinse section  68 . The slurry of water, magnetite and misplaced refuse fines from the drain section  66  is fed mainly to the first processing section  54 , with a portion fed to the second processing section  55 . The rinse section  68  of the underpan  36  will typically include less magnetite, and the slurry of water, magnetite and misplaced refuse fines from the rinse section  68  is fed to the second processing section  55 . The solid refuse particles  18  screened by the top  32  and bottom  34  screens are conventionally fed to the refuse handling section  56  via conduit  70 .  
         [0036]    Similarly, the underpan  42  of the clean coal screen section  24  is divided into a drain section  72  generally nearer the input end  51  and a rinse section  74  extending from the drain section  72  to the output end  52 . Since the clean coal  16  particles are received at the clean coal screen section as a slurry of solid clean coal, misplaced clean coal fines, magnetite and water, the majority of the magnetite will be recovered from the clean coal particles  16  in the drain section  72  of the underpan  42 , as it will simply pass through the screens  38  and  40 . However, the solid clean coal particles screened by the screen  38  and  40  will have particles of magnetite adhering thereon. To recover this magnetite, the sprayers  60  are positioned to apply water to the screened solid clean coal particles at the rinse section  74  of the underpan  42 . The magnetite and misplaced clean coal fines rinsed off of the screened clean coal particles by the sprayers  60  are received in the rinse section  74 . The slurry of water, magnetite and misplaced clean coal fines from the drain section  72  is fed mainly to the first processing section  54 , with a portion fed to the second processing section  55 . The rinse section  74  of the underpan  42  will typically include less magnetite, and the slurry of water, magnetite and misplaced clean coal fines from the rinse section  74  is fed to the second processing section  55 . The solid clean coal particles  16  screened by the top  38  and bottom  40  screens are conventionally fed to the clean coal handling section  58  via conduit  76 .  
         [0037]    The above-described screen assembly  10  has the advantage that only one screen assembly is needed for processing all three different types of feed particles. Not only does this decrease costs and save space in the preparation plant, but a plant operator can view the screen assembly  10  and immediately observe the ratio of clean coal to refuse that is present in the incoming raw coal being processed. Since it is anticipated that the clean coal slurry  16  will be greater than the refuse slurry  18 , the clean coal screen section  24  will be wider than the refuse screen section  22  to accommodate a higher volume. Using a 12′×20′ (w×l) banana screen, it is presently suggested that a partitioning of 5′ for the deslime section  20 , 2′ for the refuse section  22 , and 5′ for the clean coal section  24  be implemented. However, other screen sizes, partitioning widths, and relative feed locations are contemplated.  
         [0038]    Additionally, since the underpans  36  and  42  of the refuse  22  and clean coal  24  screen sections, respectively, are similar in construction with the recovered materials received therein passed to the same sections within the coal preparation plant  12 , the underpans  36  and  42  may be replaced with a single underpan  76  (see FIG. 2) underneath the screens of the refuse  22  and clean coal  24  screen sections.  
         [0039]    While the present invention has been described with particular reference to the drawings, it should be understood that various modifications could be made without departing from the spirit and scope of the present invention. For instance while the inventive screen assembly  10  has been described herein as a double deck banana screen, a single deck banana screen, eliminating the bottom screens, may be utilized without departing from the spirit and scope of the present invention. Further, screens other than banana screens are contemplated and may be additionally implemented. Still further, while the inventive screen assembly  10  has been shown and described herein as used in a coal preparation plant  12 , the inventive screen assembly  10  may be utilized in preparation plants for ore and minerals other than coal, using separation media other than magnetite, without departing from the spirit and scope of the present invention.