CA1064883A - Coal beneficiating process - Google Patents

Abstract

COAL BENEFICIATING PROCESS

Abstract of the Disclosure A coal beneficiating process for the efficient production of high quality coal at higher yields through a concept of stage separation which requires a minimum of crushing.

Description

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Back2round of the In~ention This invention relate~ to clas~irying, separating and assorting solids, and more particularly to coal bene-~icla~in~.
I 5 ,, Current interests ln coal bene~iciating proces~e~
'~, are directed to the problem o~ upgrading low grade ore.
With the depletion of ~ources of top grade ore~ and the ~ncreasing need to combat pollution problems as~ociated wlth the use o~ low grade (and consequently high sulfur) coal, 10 1. much interest is now centered in method~ o~ llberating coal !I from a feed which has a hlgh content o~ sul~ur and other ¦I refuse.
: -I Con~en~ional practice today includes processes ;.
' which initially completely crush all the feed to be processed 15 I to very fine sizes in order to llberate the coal ~rom both `:
1I the sulfur constituent~ and non-sulfur re~use ~clays) and ~::
tl the~eafter p~rform ~ultlple o~e~atlon~ to separate the ~ine ¦ coal from th~ reruse. U. S. Patent~ 2,319,394 and 2,330,~79 ~¦ to Erickson are examples where coal ls initlally completely 20 1l crushed to a ~ine size and therea~ter undergoes several and ¦~ ~arious ~eparation processe~ SUGh as gravity separations and sareeni~g. It has ~een ~ound ~hat gra~ity separa~lon~
¦ specifically hy~ro-cycloning, are normal means of separating oal rrom re~u~e of dlssimilar densities. Un~ortunately, the ~iner the coal and re~use~ the more dlf~icult the I ~eparatlon Or the coal ~rom th~ re~use. U. S. Patents ` -3,638,791 ~o Harri~on, 3,Q23,893 to Zabrowskl and 3,446,349 ¦ to Benzon are illustrati~e o~ the method~ currently employed ln ~ine ~oal b~n~ iat~ng pro~sse~ :

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It is, therefore, an object of this invention to provide a process which will beneficiate coal but minimize the amount of fines, both coal and refuse, whicll must be processed in the various sizing and classify-ing apparatus employed for this purpose.
Summary o the Invention We have discovered a process for beneficiating coal, particularly coal middlings, which is simpler and more efficient than the prior art. By middlings, we refer to low grade coal which is characterized by high ash about 15~ by weight and above and high sulfur about 1.75~ by weight and above. If the middlings are crushed, finer coal and refuse are released from the middlings. In the process of this invention beneficiating steps such as separating, classifying and sizing are arranged to minimize the production of a fines fraction during the course of crushing operations performed to liberate the coal from adherent refuse and middlings. Our method, unlike prior art processes, crushes ore in successive steps to -obtain increasingly smaller size with concurrent removal of coal values such that crushing and separating steps are limited substantially to the middlings fraction each time. The system increases efficiency in that larger sizes of coal and refuse are separated and removed and only middlings are continually crushed, minimizing thereby the percentage of original ore which must be classified and separated as fines. In addition to the concept of stage separation, we have discovered a combination of beneficiating steps which utilized together result in an overall improved circuit unknown heretofore.
According to the present invention, there is provided a method for recovering high quality coal from a raw coal ore feed, which feed comprises a high middlings content, comprising (a) separating a raw coal ore feed into high density mine rock and a raw feed material consisting ` -substantially of coal and middlings, ~b) discarding the high density mine rock, (c) sizing the raw feed material from (a) to recover a coarse coal product which is separated from coarse middlings, ~d) crushing the coarse ;middlings from ~c) to provide a feed ranging in average size from inter-$

: :- .. .: . . .-mediate to fine, ~e) sizing the fced from step (d) at a finer mesh than the sizing of step ~c) to recover an intermediate sized coal product which is separated from an intermediate sized middlings, ~f) crushing the intermediate sized middlings from (e) to a fines size to provide a fines feed including coalJ middlings and high density refuse, (g) separating the fines feed from step (-f) to produce a fines product frac~ion and a refuse fraction, (h) treating the product fraction from step (g) by a flotation step to recover coal, (i) separating the refuse fraction from ~
step (g) to produce three separate material fractions, including fine : :
sized coal values which are recovered~ refuse which is discarded and :~
middlings, and (j) crushing the middlings of step (i) and recycling the crushed material to step (g).
The present invention may be better understood from a con-sideration of the following drawings and exemplary embodiments.

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1()~4883 Brlef Descriptlon Or the Drawlng~ ' .
FIGURE 1 i~ a schematic repre~entation Or our p~oces~ sho~.31n~ b~neficlatlon o~ a coal middlin~s fractlon.
~ FIGURE 2 is a diagrammatic lllustratlon of an lembodlment o~ our process.
~I f Descrlptlon o~ the Prererred Embodiments The ln~tant inventlon is directed to impro~ements ln processing ~ine coal to remoYe s~lfur and ash constituents ¦ while increasirlg yield by crushing middlings. Presently in 10 1 ~he industry, there are many di~erent systems used for .
reduc~ng sulfur and a~h in fine coal 5 but all ~eature common ~:
unlt operations noted hereinbe~ore that are combined in various ways. Unlt operation~ such as hydrocyclonin~
tabling~ screening9 crushing and those that u~e classi~y~ng 1 .
15 ¦ cyclones and ~lotation are the most common. The lnstant I :
inYention presents a unique ~om~ination o~ these components , which, when working in a sy~tem~ results in impro~ed coal ~:
~ual~ty and lncreased yield.
In ~he lnstant in~ention raw coal with a top slze 2a 1l o~ several lnche~ i8 initlally 3eparated in a high density ¦¦ separator to remove a re~use that contalns no ~alus- The product ~tream from thls flrs~ separa~ionJ whl~h contains ¦
I¦ all si~es o~ coal, mlddling a~d some re~u~e, is then ~ized ¦¦ to aeparate out a ~oar3e fractlon trrom about 5" to about 25 1 1/2") ~rom the intermediate sized mater~al (about 1/2" to I about 28 mesh) and the ~ines ~abo~t 28 mesh to 0). The ¦ coarse ~aterial i8 then ~epar~ted in a low density separa~or , :
to recover a quality product (low aul~ur) and a mlddlin~

fra~tion. Mlddling i~ crushed to liberate ash and ul~ur I-. ~~- .

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10~48~3 i l i constituents rrom coal, and thi~ crushed materlal ls com-bined with the undersi~e material ~rom the first slzlng operation. Complete crushlng, where needed, is obtained ~y recirculatlng o~erslze to the cruæher ~eed. The ¢omblned material ls then ~creened to separate an lntermediate size material from the fine3. The intermediate ~ize material i8 1 i next ~eparated in a low density ~eparator to recover a quality, low sulfur product and a middling. Thls middling is crushed and combined with the fines. I
The total raw coal would normally be kreated a~ ¦
described only i~ the low density fractlons are low in sulfur. When the low density material ia high in sulfur, all the material ~n the product stream from the first ~eparator i~ cru~hed to a finer size.
Raw and crushed ~ines are trea~ed ln primary hydrocyclones which make an initial product separtion. - -R~ the lne~fi¢iencles o~ hydrocyclone separations ~coal lost to re~use and re~use mi~placed to coal), au~-iliary back up syst~ms are requlred. To cope ~ith 20,l inefficiency3 we have found ~hat good results can be achieved by (l) uslng secondary hydrocyclones to reclean the product (over~low)~ and ~2) using ~able~ to re~ect fine 8ul~ur, to recover coal lo~t to re~use (under~low~ and to recover a mlddllng which can be ¢rushed and retreated to lncrease yield. ~he secondary hydrocy~lone product ~o~erflow3, however, may 8~ill contain ~ome misplaced fine, high-density sulfur components and to re~eck these fines, we u~ cyclones ¦
which classi~y by partlcle ma8~ Heavy dens~ty ~ines and ht d glty coar~er ~lz~ are collect~d to u~derrlow, ~.
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~and thi~ stream i~ ~ized-to separat~ product ~rom ~ine sul~ur components. Cyclone over~low ls then ~ent to ., I
~lo~ation to ellmlnate hlgh ash impurlties ~rom the product.
Il Referring now to the FIGURES, and particularly to IFIG. 1, a raw coal feed ln all ~lze ran~es i~ subJected to a high density separator to remove a high denslty refuse of, l ~or example, mine rock. The feed 1~ then sized to separate ¦ a coar3e ~ractlon ~rom the feed. The coar~e ~raction ls : ~ub3ected to a low density separatlon to generate a coarse 10 ¦ coal product whioh i~ recovered and a mlddlings ~raction which ls crushed and returned to the clrcuitO At this Juncture ln the proce~s the coarse sizes o~ both coal and refuse have been fully processed and the feed is now o~
¦ ~ntermediate ~ize. The ~eed now comprises a combination o~
15 ¦ the crushed middlings and the underslzed fraction from the ¦
.¦ initial ~creenings and ls now sub~ected to a second sizin~ ~
~tep to sep~rate tbe interm~diate s~ze~ ~rom the ~ines. The ¦ :
¦¦ intermediates are separated in a low density separator to I :
¦I generate a coal product of lntermediate size and an ~nter-mediate fractlon comprlsing mlddllngs and any re~u~e. The mlddllngs and any refuse that was liberated in the first crushing are cru~hed and returned to the clrcuit where : they are combined ~ith the underslzed fraction from the second slzer, ~o ~orm a ~eed which ls generally fines. The ~ines now proceed to a rir~t hydrocyclone whlch perrorms first a combined densl~y an~ ~ize separatlon. ~he o~er~low ¦ from the ~ir~ hydrocyclone, containing generally ~iner ¦ average size than the underrlow, may be further clas~ified 1 ~:
in a 3econd cy~lone and the products o~ the ~¢ond cyclone ¦ :
3Q ¢las~ ation re~ined by ~lotation (~or the o~er~low3 and aizing (ror the underflow).
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The hydrocyclone step al~o generate~ an under~low ,whlch ls subJected to concentrat:ln~ table~ to reflne a coal pr3du_t, re~u~^ and mlddlln~s. '~he ~lrst. two, ~hat is the I!coal product and re~use, exlt the circuit and the middlings 1 ~ :
5 llare ¢rushed and recycled.
In a more detailed descr2ptlon o~ our process, and referrlng now to FIGURE 2, a raw coal feed o~ a top size o~
,about 5" and an ore content comprlslng, generally coal, I
: ¦middling and refuse i8 subJected to treatment ln a Jig 10 ~0 ::
lO separate refuse ha~ing a SpeGi~iC gravity above abou~ 1.80 1-comprising mostly mine rock. Feed material having a speclr~c gravity les~ than about 1.80 is sent to a screen 14 as shown l. .
ln li~e 12. Screen 14 ~izes the ~eed at about V 2" lmore or -. less~ and the o~ersize travels by line 16 to heaYy media ¦ ;
: 15 vessel 18. Heavy media vessel 18 separates the feed at a ~peci~ic gra~ity of about 1.30 to produce a coarse coal product o~ about 5~' to about l/22' size and a simllarly ~lzed mlddlings ~raction that has a speci~i¢ gra~ity heavier than I about 1~30 but llghter than about 1.80. The middlings I ~raction is sent by line 20 to a crusher 22 and rrom there the crushed fraction 19 combined with the minus V2t1 size ¦1 feed ~rom screen 14. The comblne~ ~eed, now line 26 is ~creened on ~creen 28 at about 28 mesh. The plu~ 28 mesh ¦ æize ~rac~ion~ from screen 28 tra~els by llne 30 to heavy ¦ medlum cy~lone 32. Heavy medlum cyclone 32 separate~ the eed to yield an intermediate slze coal product o~ about l V 2" bD 28 mesh and an in~ermediat~ ~lze mlddlings that has a : ~peal~ic graY~ ty hea~ier than about 1.33. The mi~dling~
~raction leave~ cy¢lone 32 ln line 34 and enters crusher 36.

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4~ ~3 The crush~d mlddlings exit cru~her 36 by line 35 and are comblned ln line 38 with the minu~ 28 mesh ~lnes from llne 2~ which come fro~ screen 28 comprising flne coal, ll fin~ middling~ and rlne reru3e. O~er31~e m~tcrlal can be ; 5 1l recycled as needed to the cru~her 36 by llne 37.
Hydrocyclone 39 processe~ the ~ine~ ~ractlon slurry 38 to ~eparate an over~low rraction 40 comprl~lng l I mainly 28 me3h to 0 f~ne coal and ~ome ml~placed 150 mesh : to 0 very fine refuse from the under~low fraction 46 compri~ing 10 ! malnly 28 me~h to 0 ~lne refuse and some mi~placed 28 to , -100 mesh ~lne coal. Although the system is e~fective uslng only one hydrocyclone 39, additional Gta~es of hydrocyclone3 : will lmprove the e~flciency o~ the proces~ as will be under-stood by tho~e skllled in the art. The fine coal slurry 40 i~ retreated ln a classi~ylng cyclone 41 to ~eparate an ¦ o~rflow ~ractlon 42 comprising malnly 60 me~h to 0 coal ¦ and 200 mesh to 0 re~u3e ~rom the under~low ~ract~on 44 comprising ma~nly plu8 60 mesh coal and 150 me~h to 0 ¦ reruse~ Slurry 42 .~ retreated to remove ~he contamlnating ~0 ¦ refuae flnes by a ~lotation stage 50 and ~eparate a f~nal ~;
flne ¢oa~ product 52 rrom a fine re~use 51. Cla ~fylngi : ¢yclon~ underflow 44 lg proce~sed on screen 60 which separates at about 150 me~h, and recover~ a plu8 150 mesh coal product 62 and reJect~ a 150 mesh to 0 re~use 61.
Underflow ~ractlon 46 ~rom hydrocyclone 39 i~ ¦
l reprocessad ln concentratlng table 70 to recover the ml~

! placed 28 t~ 100 mesh coal ~ine~ as product 72 ~rom a ~inal re~u~e fraction 71. Table 70 can al80 be set up to reco~er l a plu3 100 me8h mlddling ~ractlon 73, whlch can be cru~he~

3o l in crusher 80 to liberate additional coal ~alues ~rom re~u~e and by llna 81 be reproce~sed ln the ~ystem beglnnlng wlth hydrocyclona 39 or a ~lmllar system. ¦

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10~4~3 ~he new proce~s provide~ an lmproved metho~ ~or reduclng the 3ul~ur and ash content ln coal, and incr~a~ln~ l4 yield while produclng a mlnimum of rlne sizes. The improve-, ment ~eatures ~tage crushing of mldd~ing~, that are nig~ in ~ul~ur content, followed by reproces~in~ to ~1~ recover the low ~ulfur and low ash coal liberated during crushlng~ (2) I¦ re~ect high sulfur components~ ~nd (3) ~eparate additlonal ¦,' middling3 that can be crushed ~o a ~lner s~ze to ~urther Il I
¦l improYe its quallty and increaæe ~erall yield.
lO I In addltlon, the system provides lmproved ~ro~
cesslng ~echnlques for treating coal flne~. We have used Xnown components (table~, hydrocyclone~, cla8~1~ying cyclones, I ~ine screens presently used ~or procesæing ~ine coal) ln : unlque combinatlons that gl~e improved sul~ur removal per- I :
15 I ~ormance a~ well as more e~icient coal recovery, than I now available ln ~he lndu~try. ¦
¦ The ~ollowing example llsts in tabular ~orm, see i ~,~ble I, th. r~Qult~ o~ ~n e~perlmental sampling of the ¦ 3tage crushin~ o~ m~ddlings. A rau coal ~eed wa3 sub~ected 20 ¦ to a hlgh den~ity ~eparator which produced high denslty mine rock, which was dlscarded, and a product ~tream. The product ~tream wa~ sized and a coar~e middlings (5" to 1/2'1) ~rsction produced whlch was subJected to a firs~ ~tage ~ crushlng operation crushlng the middlings to -l/4" slzeO I ~
25 l Sizi~g of the middllngs ~raction ~rom the ~lrst stage cru~h-ing operation resulted in a l~4n to 28 mesh product repre-¦ sentlng ~1% by wei~ht o~ the origlnal coarse middlings~raction ~eed, 28 mesh to 0 product ln the amount o~ 16%
by ~eight, 28 mesh to 0 r~ru~e of 4~. The remaining 29%
3o by welght was 1/4" to 28 mesh middllngs ~ra¢tlon havlng a relative y hlgh 2.51% sul~ur by weight and 29.0% a3h by ~elght content.

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The 29~ by welght. 1/4" to 28 me~h mlddllng ~raction remain1ng was ~ub~ected to a second stage crushing to 14 mesh to produce a 11l mesh to O coal product havlng 1ll 1. 77% by weight ~ul~ur and g. 5% by wei~ht ash content, ,l an acceptab1e relatively high quallty coal. The remaining 13~ by welght was 14 mesh to O re~use.
¦l It w111 be under~tood that ~urther proce~ln~
lncludlng addltlonal orushlrg stages may be made as deslred.

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It, i8 ~een from Table I that a coarse middllngs fraction crushed to -1/4" having 1.89g by weight Or ~ulfur , and 1..7~ by ~ ight o~ 2sh rroduces fo~lr increments. Th~
l' l ~l flrst increment wh~ch amounts to 51~ Or the coarse middlings 5 11 ~raction is withdr2wn ~rom the 3ystem and con~lsts o~ 1/4"
¦ to 28 mesh coal product haYing a sulfur con~ent o~ 1.37 ¦ by wel~ht and an a~h content of .S.7~ by weigh~ representing ¦ a usable coal product. A 15~ incremen~ o~ 28 mesh to 0 coal product con~alns 1.41~ by weigh~ sulfur and 6.6g by welght Or ash, also a usable coal product. A thlrd increment o~ 4% by welght Or the ~oarse middlings end~ up as re~u~e.
The remaining increment, which amounts to 29% of the coarse middlings feed ln this flrst stage crushing step and which ha~
a sul~ur content of 2~51% by weight and an ash ~ontent of 29.0 by weight, i~ ~ed to a second stage crushing operation a~
intermed~a~e (1/4t' to 28 mesh~ mlddlings. Crushing the lntermediate middllngs to 14 mesh results in a coal produ¢t ¦ amoun~ing to 16% o~ th~ intermediate mlddlings and haYing : ¦ a sul~ur content o~ 1.77% by weight and an ash content o~
- 20 1 9.5% by ~eight. ~he remaining 13X 1% refuse.
¦ Thus i~ 1~ seen that ~rom a coar~e middling3 ~raction havlng 1.8g~ by welght of sulfur and 13.7% by weight Or ash~ by weight of usable coal product ls recovered havin~ 1.45% by weigh~ o~ sul~ur and 6.6~ by 25 l ¦ weight o ash.
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Claims (2)

1. Claims We claim:
   l. A method for recovering high quality coal from a raw coal ore feed, which feed comprises a high middlings content, comprising:
   (a) separating a raw coal ore feed into high density mine rock and a raw feed material consisting substantlally of coal and middlings, (b) discarding the high density mine rock, (c) sizing the raw feed material from (a) to recover a coarse coal product which is separated from coarse middlings, (d) crushing the coarse mlddllngs from (c) to provide a reed ranging ln average size from intermedlate to fine (e) sizing the reed from step (d) at a finer mesh than the sizing of step (c) to recover an intermediate sized coal product which is separated from an intermediate sized middlings, rushing the intermediate sized middling from (e) to a fines size to provide a fines feed including coal, middlings and high denslty refuse, (g) separating the fines reed from step (f) to produce a fines product fraction and a refuse fraction, (h) treating the product fraction from step (g) by a flotation step to recover coal, (i) separating the reruse fraction from step (g) to produce three separate material fractions, including fine sized coal values which are recovered, refuse which is discarded and middlings, and (j) crushing the middlings of step (i) and recycling the crushed material to step (g).
2. 2. A method for recovering high quaiity coal from a raw coal ore reed, which feed comprises a high middlings content, comprising:
   (a) separating a raw coal ore feed into high density mine rock and a raw reed material which includes sizes ranging from coarse to fine and consisting substantially of coal and middlings, (b) dlscardlng the high density mine rocka (c) sizing the raw feed material from (a) to separate a coarse fraction from an intermediate size fraction and dividing the coarse fraction at low density to recover a coarse coal product which is separated from coarse middlings, (d) crushing the coarse middlings from (c) to an intermediate size and combining same with intermediates from the sizing fraction of step (c) to provide a feed ranging in average size from intermediate to fine, (e) sizing the feed from step (d) at a finer mesh than the sizing of step (c) to separate an intermediate fraction from a fines fraction and dividing the inter-mediate fraction at low density to recover an intermediate sized coal product which is separeated from an intermediate sized middlings, (f) crushing the inermediate sized middling from (e) to a fines size and combining same with the fines fraction of step (e) to provide a fines feed including coal, middlings and high density refuse, (g) separating the fines feed from step (f) by hydrocycloning to produce a first overflow and a first underflow fraction, the overflow fraction comprising various fine sizes of coal and finer refuse, the underflow fraction comprising various fine sizes of refuse and some fine coal, (h) classifying the overflow fraction from step (g) to separate, by mass, the light mass particles from the heavier mass particles, the light mass particles comprising very fine sized coal and ultrafine refuse, the heavier mass particles comprising fine sized coal and very fine sized refuse, and treating the light mass particles by a flotation step to recover coal and screening the heavier mass particles to recover coal, (i) separating the first underflow fraction from step (g) to produce three separate material fractions, including fine sized coal values which are recovered, refuse which is discarded and middlings, and (J) crushing the middlings of step (1) and recycling the crushed material to step (g).