US 3192068 A
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Description (OCR text may contain errors)
June 1965 M. w. BRANDT 3, 92,
METHOD AND APPARATUS SYSTEM FOR GQNTINUOUSLY WASHING AND DRYING SOLID COMBUSTIBLE MATERIAL Filed Aug. 2 1961 5 Sheets-Sheet 1 Fluidized Bed Sizer Classified Fine Coal Coarse Coal 8mm Containin fine silica and other silica, s ate impurities and other impurities Prima D C clone Apex Discharge Exit gas Fine Classified Coal Product Seconds D C clone Hashing Station Apex Discharge Exit gas carrying coal dust as fuel for Fine Classified Fluidized Bed Coal Product Dryer Fluidized Bed Dyer Clean Dry Coal Stack gas to 0 clone station Clean Dry Coal Exit gas Mfll-ILON M E R/var 5y: 0 130044, 70%:456.
flhj/ June 1965 M. w. BRANDT 3,192,068
METHOD AND APPARATUS SYSTEM FOR CONTINUOUSLY WASHING AND DRYING SOLID COMBUSTIBLE MATERIAL Filed Aug. 2, 1961 3 Sheets-Sheet 2 INVENTOR K0 r I MAHLO/V WBRA/VOT ATTORNEY June 1965 M. w. BRANDT 3,192,068
METHOD AND APPARATUS SYSTEM FOR CONTINUOUSLY WASHING AND DRYING SOLID CQMBUSTIBLE MATERIAL Filed Aug. 2. 1961 s Sheets-Sheet :s
INVENTOR MAHLO/V W BRANDT y i zodom ATTORNEY United States Patent 3,192,068 METHOD AND APPARATUS SYSTEM FOR IGN- TINUOUSLY WASHING AND DRYING $01.11) 'COMBUSTiBLE MATERIAL Mahlon W. Brandt, South Salem, N.Y., assignor to Dorr- Oliver Incorporated, Stamford, Conn, a corporation of Delaware Filed Aug. 2, 1961, Ser. No. 128,851 9 Claims. (Cl. 134-25) This invention relates to a system for continuously drying solid combustible material, and more particularly to improvements in washing and drying coal or the like using fluidized solids technique whereby the solids being treated are suspended in an upwardly moving stream of gas forming therewith a dense turbulent so-called fluidized bed.
Hitherto it has been the customary practice to take the raw coal as received from the mine and subject it to various cleaning operations, most of which involve washing the coal with water so as to remove the impurities normally associated with the coal. The wet coal was then classified into a coarse fraction and a fine fraction; the coarse fraction was dried by any of the conventional drying means, the fine fraction was either discarded or treated to recover fine coal values.
However, any treatment of the fines at this stage became an expensive and time consuming operation since the fine fraction during washing became associated with a substantial amount of water. Another disadvantage inherent in the practice heretofore employed was that during washing the impurities as well as fines and coal dust would adhere to the coal and pass into the dryer thereby placing an extra burden on the drying operation. Also it was not uncommon to find that these fines were discharged from the dryer with the end product, which would thus fail to meet minimum requirements and involve objectionable dust evolution in the handling.
It is therefore an object of this invention to provide an eflicient method and apparatus for economically drying coal in the sense that both a clean coarse coal fraction and a clean fine coal fraction are obtainable both substantially dust free with a minimum amount of drying heat required.
To attain the foregoing object the invention provides a treatment system wherein raw crushed coal is first continuously classified into a'coarse fraction, including certain impurities, and a fine fraction by subjecting the mixture'to treatment in the fluidized bed of a sizer unit by an uprising stream of fluidizing air which carries the fine fraction out of the unit.
The coarse fraction, continuously removed from the bed of the sizer unit, is conveyed to a washing station for effecting the removal of the impurities whereupon the washed coarse fraction, practically free of objectionable fines, is subjected to treatment in the fluidized bed of a dryer unit employing hot combustion gases as the fluidizing medium.
The fine fraction entrained in the fluidizing air stream leaving the sizer unit comprises fine coal of saleable size as well as coal dust which is objectionable if present in excess of a permissible amount. According to the invention this mixture is passed to a primary cyclone station wherein a fine size of saleable coal product is separated. The exit air containing the coal dust is transferred to a secondary cyclone station wherein the coal dust in turn is separated in order that it may be supplied as fuel to the dryer unit at a controllable rate while exit air carries away the extremely fine particles.
According to one feature the exit air from the secice ondary cyclone along with the extremely fine coal particles provides combustion air when introduced into the combustion chamber of the dryer unit.
Another feature lies in certain improvements in the apparatus and operation of the dryer unit and more particularly in a Zone wise temperature control or controlled temperature gradient in the combustion chamber or wind box of the unit.
As this invention may be embodied in several forms without departing from the spirit or essential characteristics thereof, the present embodiment is therefore illustrative and not restrictive since the scope of the invention is defined by the appended claims rather than by the description preceding it, and all changes that fall within the metes and bounds of the claims, or of forms that are their functional equivalents are therefore intended to be embraced by those claims.
In order that this invention may be readily carried into effect and more completely understood this invention will now be described with reference to the accompanying drawing which illustrates a preferred embodiment of this invention.
FIGURE 1 is a schematic flow diagram of the process of this invention, particularly indicating the products at each stage of the operation.
FIGURE 2 is a diagrammatic arrangement of the system embodying the invention of FIGURE 1, featuring the cooperative relationship between the sizer unit, the dryer unit, and the coal washing station.
FIGURE 3 is a flow diagram exemplifying a suitable washing station in the treatment system of FIGURE 2.
Referring to the drawings and more particularly to FIGURES 1 and 2 exemplifying the invention raw coal from the mine, crushed for example to provide a mixture of approximately by zero mesh feed indicated by the letter R is screened to remove any particle size larger than 4" and then deposited via conduit F into a raw coal feed bin 10 from which it is fed into a classifying device or sizer unit 12 by means of a screw conveyor 11. The oversize coal in this example having a particle size about 4" by /1 is conveyed from the screen 29 through conduit 3%} to a heavy media separating station for example in the nature of a Chance Cone furthermore to be described.
The sizer unit 12 contains a fluidized bed 13 supported on a gas permeable constriction plate 14 through which passes fluidizing air supplied at a suitable operating pressure as from a blower 15 and fed into the windbox 19 of the sizer unit through a control valve 17. The sizer unit 12 has an expanded freeboard space 18 above the bed suited for the particular sizing operation, preferably designed and shaped in a manner shown and described in co-pending US. application of Heath and Aconsky, Serial No. 114,234, filed June 1 1961.
Fluidizing air from the Windbox 19 rises through the constriction plate so as to maintain the bed 13 in its fluidized state. This rising stream of air serves a dual purpose in that it fluidizes the particles in the bed while classifying them into a fine coal fraction and a coarse coal fraction. The velocity or so-called space rate of the fluidizing air is adjusted so that it will entrain those solid particles that are larger than the coarse coal size desired to be separated and then washed. As the air moves into the expanded freeboard space of the sizer unit there is a reduction in the space velocity of the air causing the larger particles to fall back into the bed while the smaller particles having a settling rate lower than the space rate of the fluidizing air are carried out of .the unit with the spent fluidizing air still under a pressure suited for further separating treatment as in cyclones or the like.
The size of the solids carried out of the sizer unit by enoaoee 3 the fiuidizing air is governed primarily by the space rate of the air, the specific gravity of the Solids and the shape of the particles. By regulating the space rate of the fluidizing air it is therefore possible to control a size separation as between the coarse coal fraction and the fine coal fraction.
With the above noted raw feed coal mixture of %1" by zero mesh, for example, when the sizer unit is operated at about 65" water pressure in the windbox with a bed depth of about12" and with a space rate of the fluid izing air in the freeboard space of about 6' er second all particles sizes smaller than 48 mesh will be carried out or" the sizer unit with the spent fiuidizing air.
The coarse fraction falling back from the expanded freeboard space into the bed is continuously removed from the sizer unit as through a discharge conduit 21 at a controlled rate as indicated by the discharge valve 22. The coarse coal *fractionof about by 48 mesh including the impurities is conveyed through conduit 23 to a Washing station 24 indicated generally in FIGURE 2 and more detailed in FIGURE 3.
The moisture content of the coal received from the mine isnormally in the order of 3%. lowever, since the moisture at times exceeds this amount the sizer unit may be provided with an auxiliary gas heater or the like (not shown) for raising the temperature of the fiuidizing air and accordingly reducing the moisture. it has been found that with a moisture content in excess of 3% in the raw coal feed the efficiency of the sizer unit is impaired for the reason that an excess of fine coal particles conduit 52 having control means54 into a closed receiver hopper 53. Should an excess amount of fine coal be collected by the secondary cyclone 44, then the excess may be diverted through a conduit 55 by the operation of valves 54- and 56, and be discharged by combining with the line coal product derived from the primary cyclone station 4-0.
The exit carrier air from the secondary cyclone 34 carrying fines and coal dust particles is conveyed through conduit 57 to the coal dryer 6% and according to this invention is disposed of by combustion in the windbox 62 of the dryer unit.
Dryer unit 6% comprises a drying compartment 61 proper and an air heating chamber or windbox 62 b th will tend to adhere to the coarse coal fraction delivered by the sizer unit and pass into the washing station; eventually to reach the dryer unit where the wet fine particles or wet dust places an excess evaporating load on a drying operation, While also increasing the load upon the subsequent cyclone station intended to remove fiy ash or the like from the spent fluidizing combustion gases.
The spent fluidizing air from the sizer unit carries the total fine fraction, for example of about -48 mesh, comprising fine coal particles mixed With coal dust. This mixture is conveyed through conduit 25 and enters the primary cyclone station 40, where a portion of fine coal, for example, of about 48 by 100 mesh, is separated from still finer particles or coal dust, the fine coal particles being discharged at the apex 41 of a cyclone unit through a conduit' tla presenting a fine coal product suitable for sale. The rate of apex discharge of fine coal product can be regulated .as indicated by control valve 43.
The undersize from cyclone station 44 comprising fines or dust for example of about 100 mesh pass via a conduit. 45 to a secondary cyclone station 44 where the dust is largely separated as apex discharge 50 and through a control valve 54 discharged into a receiver tank or closed hopper 53 providing the fuel supply for the operation of a dryer unit 60 furthermore to be described.
The operation of the secondary cyclone 44 provides a controllable supply of fuel in the form of coal dust for the pulverized fuel burner- 75 of the dryer unit 6%. However, depending upon the nature of the crushed coal feed there may be occasions when the exit air leaving the primary cyclone 49 may contain insuificient fuel in the form of coal dust for dryer unit 64). This deficiency may be corrected by automatically interferring with the separating eificiency of the primary cyclone by introducing a disturbing small amount of air from blower 15 into the apex section 41 as indicated by a branch. conduit 46, with the intent of such impairment controlled by means of valve 47. In this way some of the fine coal normally collected at the apex 41 is carried to exit from the primary cyclone 40 along with the spent stream of air for further disposal in the secondary cyclone station 44 providing the fuel for the dryer burner 75.
In the secondary cyclone station another separation is effected in that fine coal normally in the form of coal dust is collected at the apex 50 and discharged via a chambers being separated by gas permeable constriction plate 63. The drying compartment 61 contains a fluidized bed as supported upon the constriction plate 63 and maintained in a fluidized condition by hot drying gases rising from the windbox 62 under pressure through the constriction plate.
-Washed coarse coal from the washing station 24 is conveyed through a conduit 39 to dryer feed bin 65 and thence at a control rate into the drying compartment 61 as indicated by a feed screw conveyor 66. It is preferred that the Washed coal be introduced into the drying chamber at a point above the bed level in order that the Wet coal lose some of its moisture before it reaches the fluidized bed itself. The coal is then fluidized in the bed and dried by the stream of hot gases forced upwardly through the constriction plate.
The windbox 62 comprises a combustion zone 67 provided with the aforementioned fuel burner 75 for producing the hot drying gases. Combustion air is supplied to the burner '75 through a conduit 68 as from a blower 73,
Q the supply being controlled as indicated by a valve 73.
Since the windbox of the dryer unit operates ,under a positive pressure for example of about 1 p.s.i.g. a booster blower as may be provided to insure an adequate supply of air .to the combustion zone.
Fuel for combustion is supplied to the burner 75 from supply hopper 53 in the form of line coal or coal dust derived from the aforementioned cyclone station 44. The line coal is conveyed through conduit 8? and through a control valve 82 into aburner supply tube 81 provided with carrier air from booster blower, 83. The booster blower 83 is provided to insure adequate pressure at the windbox for the air supplied by main blower 73. The amount of carrier air'blown into the burner with the dust is controlled by means of a valve 86. Under practical operating conditions the combustion temperature provided in this portion of the combustion zone 67 of the Windb x may be in the orderof 3,000 F.
Located above the burner 75 :is an auxiliary annular conduit or gas bustle pipe surrounding an intermediate portion of the windbox 62, and communicating through radial orifices 91 with an inter-mediate combustion zone 67a. Exit air from the secondary cyclone 44 carrying the aforementioned smallest coal dust particles is supplied under its own pressure to the bustle pipe 96 to provide a portion of the combustion air aswe-ll as the hot fluidizing gas. Under practical operating conditions the temperature in this intermediate zone 67a may be approximately 2,500 F.
Since this temperature is still too high for the purpose of coal drying operations tempering air is supplied to the windbox through a main air bustle pipe 92 surrounding the upper portion or zone 67c of the windbox, and communicating therewith through a plurality of radially directed orifices 93 spaced from one another along the per'iphery of the windbox wall. This additional tempering air is supplied by main blower 73 via conduit 72 provided with a valve 94 indicates that the supply may be automatically controlled. The operating temperature of the fluid-izing gas thus obtainable and suited for the coal drying operation may be in the order of 1,300 F.
The hot gases rising through theconstriction plate main- .tains the bed in a fluidized condition While at the same time drying the coal. The spent fluidizing gases with some entrained fine coal particles leave the dryer unit through conduit 95 leading to a cyclone station 96 where dust particles or fly ash are intercepted and discharged through conduit 97 provided with valve 98, while spent exit gases thus purified are released through conduit 99 into the atmosphere. The coarse dry coal fraction which remains in the bed is discharged by way of conduit 100 at a rate controlled by means indicated by a valve 101.
The dryer unit may be dimensioned for an average space rate of the drying gases of to 12 per sec-0nd to handle a wet feed of l%" by 48 mesh. Particles escaping with the stack gases of about -28 mesh are caught by the dryer cyclone '96, which may have its apex discharge product recombined with the coarse coal product delivered from the bed. However, these two portions may also be separately collected as saleablecoal products.
.The required space rate and the drying temperature in the dryer unit are controllable by the fuel feed rate and by regulating the air supply to the main air bustle pipe 92 located directly beneath the constriction plate 63.
In the present embodiment the air pressure supplied to the sizer unit is suiiic-ient to operate both the primary and secondary cyclone 40 and 44 respectively :as well as to introduce the secondary cyclone exit air into the auxiliary gas bustle pipe 90 and against the operating pressure required in the windb-ox of the dryer unit. The pressure difieren-tial between the sizer blower 15 and the dryer windbox pressure may be maintained at about 1 p.s.i.g. This pres-sure differential would correspond to the sizer blower operating :at about 2 /2 p.s.i.g. (or approximately 65 of water) and the dryer blower operating at about 1 /2 p.s.i.g. (or about 40" of water), leaving about /2 p.s.i.g. (15" of water) excess pressure at the auxiliary bust-1e pipe of the dryer unit. The pressure in the freeboard space of the dryer unit may .be in the order of 8" of water with a bed depth of about 18" containing by 48 mesh discharging as the coarse coal product from the bed. The final operating pressure at the dryer cyclone 96 may then be about 2" of water.
Referring now to the washing station as exemplified in FIGURE 3 the sizer bed product of about by 48 mesh is first screened on conventional type screen 26 from which the oversize which may be about by /8" is conveyed through conduit v27 to a heavy media separator or a Chance Cone 28 where it mixes with the oversize particles from another screen 29.
In the Chance Oone impurities associated with the oversize coal are removed and discharged to waste to a conduit 30a. The clean coal is conveyed through a conduit 31 to crusher 32 Where the coal is further reduced for example to about 1%".
The undersize from screen 26 which may have a particle size of by 48 mesh is conveyed via conduit 34 to Deister tables 33 to effect the elimination of impurities such as silica and clay, etc. from the coal and discharged to waste through conduit 35. The remaining clean coal delivered from the separation table is conveyed through conduit 36 to a filter 37 which may be a continuous rotary drum filter wherein the coal is dewatered. However a continuous rotary table filter may be preferred where the various size ranges in the coal slurry might tend to separate or stratify in the drum filter trough and thus interfer with the filter cake formation. The use of a table filter avoids that possibility for the reason that the heavy coal particles settle directly on the media of the table, thereby providing a suitable permeable base or layer for the slower settling finer size particles to collect and continue to form a filter cake without the danger of clogging the filter media.
The dewatered filter cake is conveyed through conduit 38 to be mixed with the crushed coal from crusher 32.
and then conducted to the dryer unit 60 via conduit 39.
From the foregoing it will be seen that the invention provides an economical as well as readily controllable treatment system and mode of operation, whereby crushed raw coal or other particulate combustible material including admixed impurities as well as coal dust is obtainable in the form of a clean and dust free coarse coal product with a fine coal fraction and the coal dust in the air stream from the first fluidized bed by-passing the coarse coal washing station, in order that fine coal or coal dust may serve as fuel at a controlled rate to provide the drying gases for the washed coarse coal in the second fluidized bed, preferably with separated dust carrier air utilized in the combustion.
Furthermore, while the invention has been illustrated and described as embodied in a coal washing and drying system, it is not limited to the details shown, since various modifications and structural changes may be made without departing from the spirit of this invention.
1. The method of cleaning and drying coal which comprises, continuously classifying raw crushed coal into a coarse coal fraction and a fine coal fraction in a first fluidized bed by the use of an uprising stream of fluidizing air which entrains and carrys away the fine coal fraction along with dust; continuously recovering a fine coal product by separating said fine coal fraction from the air stream carrying away the dust fraction; continuously washing said coarse coal fraction to separate impurities therefrom; continuously drying the washed coarse coal fraction in a second fluidized bed by the use of an uprising stream of hot fiuidizing gas produced by the combustion of said separated dust fraction.
2. The method according to claim 1, wherein said air stream is utilized as combustion air for said second bed.
3. The method according to claim 1, wherein said air stream carrying said dust fraction is subjected to further separation into a dust fraction and an exit air stream used to provide said combustion air, and wherein said dust fraction is utilized as fuel for producing the combustion gases at a controlled rate.
4. Apparatus for cleaning and drying coal which comprises classifying means for separating raw crushed coal in a coarse fraction and a fine fraction in a first fluidized bed means by an uprising stream of fluidizing air, provided with means for continuously removing said coarse fraction from said fluidiziug bed, and means for continuously removing said fine fraction together with the uprising stream of air from said fluidized bed; means for washing said coarse fraction so as to remove impurities therefrom; cyclone means for separating said fine fraction into a fine coal product and a dust fraction; drying means for drying said washed coarse coal in a second fluidized bed means by an uprising stream of hot fluidizing gases; and burner means for burning said dust fraction so as to generate said hot gases.
5. Apparatus according to claim 4, wherein additional cyclone means are provided for separating said dust fraction from the stream of carrier air; and means for feeding said separated dust fraction at a controlled rate to said burner means forcombustion; and means for supplying said stream of carrier air to said fluidized bed for maintaining said second fluidized bed.
6. Apparatus according to claim 4, wherein said dryer means comprises a constriction plate, a fluidized bed on sa1d constriction plate and a windbox below said constriction plate, and wherein said windbox comprises a lower most combustion zone including said burner means, an intermediate combustion zone including an auxiliary annular bustle pipe for supplying said air stream to said zone, and a top most zone comprising a main bustle pipe for supplying tempering air to said zone.
7. The method of cleaning and drying coal, which comprises classifying crushed coal into a coarse coal fraction and a fine coal fraction in a first fluidized bed by the use of an uprising stream of fluidizing air which entrains and carries away the fine' coal fraction along with dust; recovering a fine ooal product-by separating said fine coal fraction from the air stream carryin g away the dust fraction; subjecting said air stream carrying said dust 'fraction to a further separation into a dust fraction and an exit air stream fraction; washing said coarse coal fraction to separate the impurities therefrom; drying the washed coal fraction in a second fluidized bed by ,the use of an uprising stream of hot'fluidizing gas; and utilizing said separated exit air stream fraction to provide at least a portion of said fluidizing gas for said secondbed.
8. The method according to claim 7, wherein'fine dust particles carried by said separated air are'subjected to tinuously removing said fine fraction together with the-uprising stream ofai-r from said fluidized bed; means for Washing said coarse fraction so asto remove-impurities therefrom; first cyclone means for separating-said fine fraction into a fine coal product and a dust fraction leavingthe cyclone with carrier air; second cyclone means for separating said dust fraction from said stream of carrier air; drying means for drying said washed coarse coal in a second fluidized bed means by an uprising stream of hot fluidizing gases; burner means and fuel supply means therefor for generating said hot fiuidizing gases; and means for introducing said stream of carrier air into said hot fluidizing gases for maintaining said second fluidized bed.
- References Cited by the Examiner UNITED STATES PATENTS 2,586,818 2/52. Harms ,3410 X 2,638,684 5/53 Jukkola 34-10 2,763,478 9/56 Parry V 34--57 X 2,770,052 11/56 Morrison 4. 34-57 X 2,789,568 4/57 Hirst 134-56 2,956,347 10/60 Gordon H 34- 10 3,058,229 .10/62 Downing 34-136 NORMAN YUDKOFF, Primary Examiner.
CHARLES OCONNELL, Examiner.