Abstract:
In a coal preparation plant which receives a raw coal feed and separates the raw coal into clean coal and refuse, an apparatus is provided for use therein. The inventive apparatus is a combined sump common to the heavy media vessel and heavy media cyclone circuits used for recirculating medium storage for the heavy media vessel circuit and mixing device, referred to as a wing tank, to proportionally combine intermediate sized raw coal feed particles with a slurry of media and water for feeding the heavy media cyclone circuit. The advantage of this combined system is the ability to use a common recirculating media for use in both the heavy media vessel and heavy media cyclone circuits, without sacrificing the ability to have different recirculating gravities for each separating circuit.

Description:
FIELD OF THE INVENTION 
     The present invention is directed generally toward coal preparation plants and, more particularly, toward a new common correct media sump and wing tank apparatus for processing raw coal particles with a slurry of media and water. 
     BACKGROUND OF THE INVENTION 
     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. Coal preparation 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. These two processing methods include heavy media and water based separation methods. Heavy media separation, utilizing a slurry of media, e.g., magnetite or ferrosilicon and water, 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 commonly understood in the coal processing art. 
     Coal preparation plants may incorporate one or two heavy medium circuits for processing coal with a bottom size ranging from 0.5 mm to 2.0 mm. Often two separate processing methods, or circuits, are employed, namely, heavy media vessel and heavy media cyclone circuits for cleaning the coarser and finer coal size fractions, respectively. 
     Plants using heavy media processing require a pre-sized (removal of undersized and/or oversized particles) circuit feed. Raw coal screens are generally used to pre-size the correct media feed, whereas deslime screens are used to pre-size the heavy media cyclone feed, although a single screen may be used to pre-size the feed for both unit operations. 
     The raw coal screen receives the raw coal feed particles and separates them into coarse and undersized raw coal. The coarse or larger sized particles discharged from the raw coal screen surface are directed by gravity to the heavy media vessel. The deslime screen receives the undersized raw coal from the raw coal screen and separates it into intermediate and finer sized fractions. The raw coal particles discharged from the screen surface of the deslime screen are directed to the heavy media cyclone feed circuit, while the finer sized particles passing through the deslime screen are fed to the fine coal section of the coal preparation plant. 
     Traditionally, each heavy media feed circuit retains its own medium for recirculation, and thus requires separate medium storage sumps. These separate storage sumps increase the overall size of the plant area requirements, and add to the cost of building the coal preparation plant. 
     The present invention is directed toward overcoming one or more of the above-mentioned problems. 
     SUMMARY OF THE INVENTION 
     In a coal preparation plant which receives a raw coal feed and separates the raw coal into clean coal and refuse, an apparatus is provided for use therein. The inventive apparatus is a combined sump common to the heavy media vessel and heavy media cyclone circuits used for storage of the recirculating medium for the heavy media vessel circuit and a mixing device, referred to as a wing tank, to proportionally combine intermediate sized raw coal feed particles with a slurry of media and water for feeding the heavy media cyclone circuit. The advantage of this combined system is the ability to use a common recirculating media for use in both the heavy media vessel and heavy media cyclone circuits, without sacrificing the ability to have different recirculating gravities for each separating circuit. 
     The commonality between the two chambers of the combined apparatus is connecting the overflow of the wing tank to the correct media feed sump. The inventive apparatus includes a wing tank with an inlet receiving the intermediate sized raw coal directly from a deslime screen and a slurry of media and water from the drain portion of an underpan of at least one media recovery screen (refuse screen and clean coal screen) and an outlet by which the mixture of intermediate sized raw coal and slurry exits the column. The wing tank mixes the intermediate sized raw coal and the slurry of media and water according to a select proportion, and it is then pumped to a heavy media cyclone separation circuit, or section, of the coal preparation plant. 
     The inventive apparatus also includes a storage and feeding device, i.e, correct media sump, for retaining and distributing, via a pump, the recirculating medium used for the correct media circuit. The correct media feed sump includes a open top inlet for collection of the slurry of media and water from the drain portion of an underpan of at least one media recovery screen (refuse screen and clean coal screen) and an outlet by which the medium exits the sump. 
     In one form of the inventive apparatus, the wing tank is located adjacent to, or integrally formed with, the correct media feed sump, such that an overflow from the wing tank discharges into the correct media feed sump. The overflow is created when wetted intermediate raw coal particles discharged from the deslime screen are fed into the wing tank displacing an equivalent volume of media contained within the wing tank. 
     First and second nuclear density gauges may be provided for measuring the specific gravities of both the mixture output by the wing tank and the medium output by the correct media feed sump. The signals generated by the nuclear density gauges are received by control circuitry that adjusts the addition of water to the outputs of both chambers. Specifically, a water source is connected to the outputs of the wing tank and correct media feed sump via at least two control valves. The control circuitry adjusts the control valves to add water from the water source to the output mixtures based upon the measured specific gravity value of each mixture contained within the respective discharge pipes. 
     In another form, the inventive apparatus includes first and second pumps for discharging the mixture of raw coal and medium from the wing tank and medium only from the correct media feed sump. Each of the pumps has a suction connected to the respective storage device and an output connected to an input of the respective heavy media separating device, namely, vessel and cyclone separating devices. The water source is preferably connected between the respective storage device and each of the pump suctions, while the nuclear density gauges are preferably provided between the pump output and the respective heavy media separating device input. 
     In a further form, the inventive apparatus may include an over dense media splitter box, at least one bleed box, and a common medium distribution box. Over dense media from a magnetic separator, which is used to recover magnetite from the effluent streams from both of the heavy media separating circuits, is collected and distributed to the two chambers of the common correct sump/wing tank via the over dense media splitter box. The over dense media splitter box preferably contains a pneumatically controlled actuator driven by a signal generated from the plant control circuitry. 
     The common medium distribution box receives the slurry of media and water from the drain portion of the underpan of at least one media recovery screen. The bleed box is used to remove extraneous amounts of non-magnetics and water from the recirculating medium in the common medium distribution box. A quantity of the recirculating medium is bled from the system proportional to the feed contaminants. The bleed box device preferably contains a pneumatically controlled actuator driven by a signal generated from the plant control circuitry. 
     In an alternate form, the common medium distribution box may be removed and the return media proportionally fed directly to the wing tank and the common correct media sump. In this alternate form, the bleed box can be fed by any other means containing correct or return media as will be appreciated by one of ordinary skill in the art. 
     A method of combining the medium requirements for two separate media separating devices is also provided. The method generally includes the steps of receiving, at a combined wing tank/correct media feed sump, a slurry of media and water from the drain portion of an underpan of at least one media recovery screen (refuse screen and clean coal screen), receiving sized raw coal directly from a deslime screen, and mixing the raw coal and slurry in the wing tank according to a select proportion having a select specific gravity, such that overflow from the wing tank is received directly by the common correct media sump. 
     In one form, the inventive method further includes the steps of measuring the specific gravities of the outputs of both the wing tank, containing the sized raw coal and slurry mixture, and the correct media feed sump, containing a medium of water and magnetite. Additional water is individually added to the output flows of each storage unit in response to the measured specific gravities of each stream to maintain the selected specific gravity in each respective stream. Two pumps may be provided, one for feeding the sized raw coal and slurry mixture from the wing tank to a heavy media cyclone separating device, and one for feeding the media from the correct media feed sump to the heavy media vessel separating device. The pumps are generally provided between the storage chamber outputs and the input of the respective heavy media separating device. 
     Two nuclear density gauges may be provided for measuring the specific gravities of each respective flow stream. In a preferred form, the specific gravity of each stream is measured downstream of the respective pump and upstream of the respective heavy media separating device. Water is preferably added to each stream flow, in response to the measured specfic gravity value, downstream of the respective medium storage device and upstream of the respective discharge pump. 
     In another form of the inventive method, the wing tank is located adjacent to, or integrally formed with, the correct media feed sump, such that the overflow from the wing tank discharges directly into the correct media feed sump. 
     It is an object of the present invention to: 
     remove the need for a separate heavy media cyclone feed sump in coal preparation plants; 
     provide the ability to use a common recirculating media for use in both the heavy media vessel and heavy media cyclone circuits, without sacrificing the ability to have different recirculating gravities in each separating device circuit; and 
     provide a common apparatus for storage of the recirculating media and for mixing the raw coal particles and the slurry of media and water, while occupying minimal space in a coal preparation plant. 
     Other objects, aspects and advantageous of present invention can be obtained from a study of the specification, the drawings, and the appended claims. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIGS. 1-2 together are a block diagram of a coal preparation plant incorporating the inventive common correct media sump and wing tank design. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Referring to FIGS. 1-2, a block diagram of a common apparatus, shown generally at  66 , is illustrated for the storage and distribution of recirculating media to two independent heavy media separation devices, or circuits, along with other components of a coal preparation plant, the coal preparation plant shown generally at  10 . In order to better understand the inventive apparatus and method, the general operation of the coal preparation plant  10  when processing the coarser sized raw coal particles will be described. 
     The coal preparation plant  10  includes a raw coal screen assembly  11  receiving a raw coal feed  12  which includes both clean coal and refuse. The raw coal screen  11  conventionally separates the raw coal feed  12  into coarse  13  and finer  15  sized coal fractions. The coarse coal fraction  13 , which is discharged from the raw coal screen deck as oversized coal, is gravity fed to a heavy media vessel  14 . The finer sized coal fraction  15  is received in an underpan (not shown) of the raw coal screen  11  and fed to a deslime screen  16 . The deslime screen  16  conventionally separates the finer size coal  15  from the raw coal screen  11  into intermediate sized coal  17  and fines  18 . The fines  18  are directed to conventional fine coal processing circuitry  19  of the coal preparation plant  10 . 
     The raw coal coarse size fraction  13 , via gravity, and the vessel recirculating medium  50  (described in more detail hereafter), via a pump  37 , are fed to the heavy media vessel  14 . The heavy media vessel  14  conventionally separates the raw coal  13  into clean coal  52  and refuse  54 , with each reporting to media recovery screens  20 , typically of the vibratory type. The media recovery screens  20  include clean coal and refuse media recovery screens having drain  56  and rinse  58  sections. The majority of the magnetite, or ferrosilicon, used in the separation process will be recovered from the refuse  54  and coal  52  particles in the drain section  56  of the media recovery screens  20 . Magnetite that has not passed through the media recovery screens  20  to the drain section  56  will be rinsed off of the respective clean coal/refuse particles and received in the rinse section  58  of the medium recovery screens  20 . The drain section medium  21  is directed to a common medium distribution box  23 , and the rinse section dilute medium  22  is fed to a magnetic separator media recovery device  24 . 
     The raw coal particles  17  screened by the deslime screen  16  are received directly at the coal inlet of a wing tank  25 . These raw coal particles  17  are mixed with a slurry of media and water in the wing tank  25  to form a raw coal slurry  94 . The raw coal slurry  94  is fed, via a pump  26 , to a heavy media cyclone separating device  27  which utilizes conventional coal processing techniques to produce clean coal  28  and refuse  60 . The clean coal particles  28  and refuse particles  60  are individually fed to vibratory media recovery screens  29 . The media recovery screens  29  include clean coal and refuse media recovery screens having drain  62  and rinse  64  sections. 
     Since magnetite is typically utilized as the media by the heavy media separating device  27  for separating the clean coal  28  from the refuse  60 , the clean coal  28  and refuse  60  particles passing over the media recovery screens  29  will both include particles of magnetite thereon. The majority of the magnetite will be removed from the refuse  60  and coal  28  particles in the drain section  62  of the media recovery screens  29 . Magnetite that has not passed through the media recovery screens  29  to the drain section  62  will be rinsed off of the respective clean coal/refuse particles and received in the rinse section  64  of the medium recovery screens  29 . The drain section medium  30  is directed to the common medium distribution box  23 , while the rinse section dilute medium  31  is fed to the magnetic separator media recovery device  24 . 
     The clean coal particles screened by the media recovery screens  20  and  29  are passed to conventional clean coal handling section(s) (not shown) of the coal preparation plant  10 , while the refuse particles screened by the media recovery screens  20  and  29  are passed to conventional refuse handling section(s) (not shown) of the coal preparation plant  10 . 
     The media  21  and  30  received by the distribution box  23  is proportionally fed to the wing tank  25  and a correct media feed sump  32 . It should be noted, however, that the distribution box  23  shown in FIG. 1 may be removed and the return media  21  and  30  may be proportionally fed directly to the wing tank  25  and the correct media feed sump  32 , without departing from the spirit and scope of the present invention. In this embodiment, the bleed box  40  can be fed by any other means containing correct or return media as will be appreciated by one of ordinary skill in the art. 
     The wing tank  25  and correct media feed sump  32  are integrally formed, or common to one another, such that the overflow from the wing tank  25  flows into the correct media feed sump  32 . The combined wing tank  25  and correct media sump  32  design, such that the overflow from the wing tank  25  is received in the correct media sump  32 , constitutes the inventive apparatus, shown generally at  66 . 
     Since the amount of medium and coal fed to the wing tank  25  will exceed the total volume discharged by the heavy media cyclone feed pump  26 , an overflow condition exists, shown by arrow  68 , from the wing tank  25  to the correct media feed sump  32  The medium returned to the wing tank  25  is also split such that approximately fifty-percent of the total wing tank medium is fed to the central column of the wing tank  25  and fifty-percent to an overflow chamber  33 . The remainder of the recirculating medium from the distribution box  23  is directed to the correct media feed sump  32 . The distribution of media from the distribution box  23  is described below. 
     The distribution box  23  conventionally separates the media received therein into four media flows  70 ,  72 ,  74  and  76 . The media flow  70  from the distribution box  23  is fed to the correct media sump  32 . The media flow  72  from the distribution box  23  is fed to a bleed box  40  through a conventional hand switch  78 . The bleed box  40  conventionally separates the media into two media flows  80  and  82 . The bleed box  40  is preferably an elephant trunk distribution box, however, other types of distribution boxes may be utilized for the bleed box  40  without departing from the spirit and scope of the present invention. 
     The media flow  80  from the bleed box  40  is combined with the rinse section dilute mediums  22  and  31  and fed to the media recovery device  24 . The media flow  82  from the bleed box  40  is combined with the media flow  74  from the distribution box  23  and is fed to the overflow chamber  33  of the wing tank  25 . The overflow chamber  33  includes an orifice plate  84 , and any of the media that does not flow through the orifice plate  84  and into the wing tank  25  overflows to the correct media sump  32 . The media flow  76  from the distribution box  23  is mixed with the raw coal particles  17  from the deslime screen  16 , with the slurry of coal, media and water received at the coal inlet of the wing tank  25 . 
     The media recovery device  24  recovers over dense media  86  from the received media flows, and outputs the over dense media  86  to an over dense media splitter box  35  through a hand switch  88 . The over dense media splitter box  35  is similar in construction to the bleed box  40  and conventionally separates the over dense media  86  into two over dense media flows  90  and  92 . The over dense media flow  90  from the splitter box  35  is fed to the correct media sump  32 , while the over dense media flow  92  from the splitter box  35  is fed to the wing tank  25 . 
     The specific gravity of the raw coal slurry  94  feeding the heavy media cyclone  27  is measured by a nuclear density gauge  38 . The nuclear density gauge  38  generates a signal representative of the measured specific gravity value, which is received by plant control circuitry  96 . The plant control circuitry  96 , in response to the measured specific gravity value, conventionally controls a make-up water control valve  34  to proportionally add water from a water source  98  to the suction piping of the heavy media cyclone feed pump  26  to maintain the specific gravity of the raw coal slurry  94  to a selected point. In addition, the control circuitry  96  conventionally controls the over dense media splitter box  35 , which receives over dense media recovered by the magnetic separator  24 , to proportionally add a portion of the over dense media received in the over dense media splitter box  35 , via over dense media flow  92 , to the wing tank  25  to aid in maintaining the specific gravity of the raw coal slurry  94  to the selected point. 
     Similarly, the specific gravity of the recirculating medium  50  fed to the heavy media vessel  14  is measured by a nuclear density gauge  39 . The nuclear density gauge  39  generates a signal representative of the measured specific gravity value which is received by the plant control circuitry  96 . The control circuitry  96 , in response to the measured specific gravity value, conventionally controls a make-up water control valve  36  to proportionally add water from the water source  98  to the suction piping of the correct media feed pump  37  to maintain the specific gravity of the recirculating medium  50  to a selected point. Additionally, the control circuitry  96  conventionally controls the over dense media splitter box  35  to direct the remaining portion of over dense media, via over dense media flow  90 , from the over dense media splitter box  35  to the correct media feed sump  32  to aid in maintaining the specific gravity of the recirculating medium  50  to the selected point. 
     If the specific gravity of the recirculating medium  50  is still too low, the control circuitry  96  conventionally controls the bleed box  40  to bleed additional medium at media flow  80  to the media recovery device  24  to add additional medium to the recirculating medium  50  to maintain its specific gravity at the selected point. A conventional level sensing device (not shown), which is part of the plant control circuitry  96 , monitors the level in the correct media sump  32 . If the level in the correct media feed sump  32  falls too low, then additional dry magnetite is added from a dry magnetite storage bin  41 , via a screw conveyor  42 , to the correct media feed sump  32 , as controlled by the level sensing device. 
     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 example, while the correct media sump and wing tank are shown in the drawing as being integrally formed, they may also be connected via chutework such that the overflow from the wing tank is received by the correct media sump. Further, the inventive correct media sump and wing tank design may be utilized in preparation plants for ore and minerals other than coal, using separation media other than magnetite or ferrosilicon, without departing from the spirit and scope of the present invention.