CA1142755A - Process for drying organic solid materials using steam - Google Patents

Process for drying organic solid materials using steam

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Publication number
CA1142755A
CA1142755A CA000362321A CA362321A CA1142755A CA 1142755 A CA1142755 A CA 1142755A CA 000362321 A CA000362321 A CA 000362321A CA 362321 A CA362321 A CA 362321A CA 1142755 A CA1142755 A CA 1142755A
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CA
Canada
Prior art keywords
water
drying
suspension
steam
solid material
Prior art date
Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
Expired
Application number
CA000362321A
Other languages
French (fr)
Inventor
Alois Janusch
Franz W. Mayer
Current Assignee (The listed assignees may be inaccurate. Google has not performed a legal analysis and makes no representation or warranty as to the accuracy of the list.)
Voestalpine AG
Original Assignee
Voestalpine AG
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Priority to ATA6711/79 priority Critical
Priority to AT0671179A priority patent/AT363905B/en
Priority to AT0739779A priority patent/AT369423B/en
Priority to ATA7397/79 priority
Application filed by Voestalpine AG filed Critical Voestalpine AG
Application granted granted Critical
Publication of CA1142755A publication Critical patent/CA1142755A/en
Expired legal-status Critical Current

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Classifications

    • FMECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F26DRYING
    • F26BDRYING SOLID MATERIALS OR OBJECTS BY REMOVING LIQUID THEREFROM
    • F26B7/00Drying solid materials or objects by processes using a combination of processes not covered by a single one of groups F26B3/00 and F26B5/00
    • CCHEMISTRY; METALLURGY
    • C10PETROLEUM, GAS OR COKE INDUSTRIES; TECHNICAL GASES CONTAINING CARBON MONOXIDE; FUELS; LUBRICANTS; PEAT
    • C10FDRYING OR WORKING-UP OF PEAT
    • C10F5/00Drying or de-watering peat

Abstract

A b s t r a c t The process for drying as well as for, if desired, modification of the structure of organic solid material, such as for example brown coals, is using steam as the drying agent. The organic solid materials have their upper grain size limited to approximately 50 mm and are suspended in water and heated under a pressure exceeding atmospheric pressure. It is already when preparing this suspension that a first pre-drying is effected. In the following the selected operating pressure exceeding atmospheric pressure is maintained or increased and the suspension is centri-fuged in at least one further drying stage. In all drying stages succeding the stage in which the suspension is pre-pared heating is effected by supplying steam. The suspended solid materials are continuously discharged from the last drying stage maintained under a pressure exceeding atmospheric pressure and pressure-released.

Description

. ~
11~;2755 The present invention refers to a process for drying organlc solid materials, particillar]y brown coals, by using steam. It is known th~t the frequently considerable content of the brown coal in humidity consists for a considerable portion of chemically bound w~ter and of water c~ptllred within the pores OL` the brown coal and that this water can be removed from the coal only with a high expenditure in energy when directly heAting the coal. ]t is also kno~m that this water can be expelled from the brown coal by means of steam but also by means of hot water. rl'here are also known processes which allow to dry the coal in a semi-contin-lous manner. Such ~nown processes give, in most cases, a substantially better use of the energy sup~lied than the basic ~`leiBner-process but the problem of dewatering the coal has only been solved in an tm-satisfving manner with the known processes.
It is an object of the present invention to provide a process which allows to efficiently dry and further carbonize the coal by removAl of carboxy groups, respectively, in a particularly economic manner and with an only low energy require-ment and which simult~rleously gives rise to only minor problems with waste water. ~or solving this task, the invention essentially consists in that the organic solid materials are in their original condition or in form of preshaped bodies of a maximum grain size of approximately 5Q mm continuously sus-pended with water and heated un~er an operati,ng pressure exceeding atmospheric pressure in a first drying stage 7 in that the susperlsion is subsequerltly passed through at least ll~Z'~55 one succeedi.ng drving <;-tnge thereby maintai.nir~g or increasing the operating pressure exceeding atmospheric press~e and centrifuging the susI)ension in at least one succeedi.ng drying stage and heating the suspension in all succeeding drying stages by supplying steam and in that thereupon the separated solid materials are continuously discharged lrom the last drying stage maintai.ned under operating pressure and are pressure-re-leased, whereupon drying is terminated under aeration. In view of the grain si7.e being limited with approximately 50 mm, the individual particles cc~ more rapidl3r be heated over t~eir whole cross section so that the residence time can be reduced as well as t~le energy consumption can be lowered. In view of preparing the suspension under a pressure e~ceeding atmospheric pressure and with increasing the temperature, this first process step is alread~r effective as a dryirlg step. In view of centrifuging the suspension in the steam atmosphere of the sai.d at least one drying stage succeeding the mentioned first drying stage, the drying capacity can substantially be increased wit}~ simultaneous reduction of the energy consumption, because the particles of solid material become plastic at the high temperatures of' the steam atmosphere what results in a favourable shrinking tendency of the solid material. ~imultaneously, the remova~ of water from the interior of the coal particles is accelerated under the action of centrifugal forces. By subdi.vi.ding the process into a plurality of stages,a smooth progress of the continuous process is achieved and the particles of solid material have, as compared with coals dried accord~ng to known processes, a sl~bstantially lower w~ter content i.n view oJ' their high shrinkage after having been pressure-released and discharged, respecti.vely, md post-dri.ed with aeration. rl`he coal dried according to the inventive process is, i.n view of carboxy groups having been removed to a vast extent, h~,rdrophobic in natllre And scarcely absorbs water.
It is adv~nt~geous to pass the suspension, prior to centri-fuging, over sieves, particularly slot sieves. In this manner the proportion of the process water dragged from one drying stage to the succeeding drying stage is substantially reduced and the conditi.ons are optinized under whic}l the steam atmosphere can become effective. In thi.s manner the contact between coal and steam is i~proved and the heat transmission is accellerated.
Simult~meously, the energy requi.rement is reduced, because excessive process water can be discharged in a simple ~lanner, for ex~lmple via locks, and need not be heated in t~le s~lcceeding drying stages.
When performing the drying process it is of particular advantage to vent the C02 produced in the indi.vidual drying stages. The C02, which is created during the progressing car-bonization, forms a gas cushion in the autoclaves and c~ntri-fuges and acts as a heat insulation w~ich prevents t~!e steam atmos~here to becor!le effective as far as possi.ble. l`his un-desired effect mut be eliminated by venting the C02. Venting of C2 is preferablv eff'ected in the fi.rst drying stage, in which the suspension is prepared, at a position c~.osely above the liquid level of the suspension.
~ 'or.a favol1rable energy balance it i.s of advar.tage also to make llse of the heat content of the process water in several ll~Z755 respects. In a particular éldvantageous manner, the process water is supplied into a sedimentation container, in particular into an upstre~m classifyer, whereupon the proportion of t~e process water~whic}l is enriched in solid materia]., is returned into a drying ~t~ge. By SUCh recycling of the propcrtion of the process water enric~ed jII solid mRterials, the susperlsion is simultaneollsly heated, noting that process water, particularly process water enriched iIl sc)]id material,is preferably supplied to the J.irst dryi.rlg 1tage in an amount which is sufficient for prep-~ririg the suspension and for he?~ti.ng the suspension to a temperitUre of at least 100 C which corresporlds to the techno-logical conditions. ~aid temperature can be selected within the range of 100 to 160 C. In view of the proportion of t~e process water enriched in solid materia].s being, ?S a rul.e, not sufficient for supplying the amount of water required for the suspension, also a porti.on of the process water depleted in solid materials is recycled. l`he proportion of the process water depleted in solid material is preferably introduced into an oxydation equip-ment in which the organicmatter is oxydized by introducing air or oxygen. In view of the heat content of the proportion of the process water enriched in solid materials being s~lfficient for heating the suspension, the process water flowirg out of the oxydation equipment can be pressure-re].eased and the he?~t content of the process water can be utiliY.ed in heat exchangers, for example for heélting th.e boiler feed water and/or air In view of additionéll water being continuously expe]led from the coal to ~)e dewatered, only a portion of t}-e process w?.ter depleted in solld material and coming from the oxydation eq~lipment must be _ ~ _ introdl~ced into -the first drying stage for contro]ling the ~rocess conditions.
'i'he process is in an adva~rLtngeous manner perfcrrrled such that in the ~r~ing stages succeeding the first drying stage a wor~ing terrperatllJe of at least 160 C is maintained. rl'he operating terrlperature can, for exc~mple, be within the range of 200 to 260 C cmd can particularly be selected wit~ approximately 245 C. In the drying stages operated with pressurized steam, the steas~ pressure is advantageously at least 8 bar, noting that the pre~surecs. can be the ~.ame but the tem~)eratures can be different. It is Wit}.OIlt furt}ler possible to work at pressures up to ~ bar.
In view of heatirlg of the coal beirlg, according to the invention, effected for a greRt extent in a steam atMosphere, t~le amount of heating fluid for heat transmission in a conden-sating steam atmosphere is substantially smaller than when transmitting heat on the coal by hot water. According to the invention it is preferab]y work~d in at least two drying stages within a steas~ atmosphere, noting that the steam cosldeslsate obtained and the water expe]led i9 extracted from the process.
By continuollsl~r discharging the process water,the heat trans-mission from t~e steas~ atmosphere to the coal is isr.proved. This is similarlv applicable for other organic materials.
In a particularly advantageous rslanner, the process according to the invention is performed such that l`our drying stages are provided, that -the second and the third drying stages are operated in a steam atmosphere, that C02 generated, ii` any, is extracted in the first and the second drying stage and that the t;}~~
solid m<ateri.als arr* dischArged i,nto fourth dr~i.ng stage. The fourth dr~ing ~tage can be o~erated urlder atmosp~erlc pressure and under suppl,~Jing of air heated by process water, noting that the fourth dr~vring stage can, for c:Y.ample, be designed as fluidized bed dr~vrin.g device.
For achieving a further re~uction of t}e heat consumption of such a process and f'or obtaining a particularly economic process performmc~ it is preXerred t.o,separate the major part of the water used for preparirlg the suspension bef`ore or after entering the fi.rst succeeding drv~ing stage and to discharge this water Wit}l detour of optiona].ly provided further drying stages from the stages mairltai.ned under operati.ng press~lre and/or to .recycle thi.s water into the first dr~ring stage in which the suspension is prepared.
In view of separatinn of the process water a].ready being effected ~t an ear]ier Moment ' ;n a dewatering stage or after entering the first succeedi.ng dr~ing stage, the suspension water alread~ cooled by h~ving transmitted its heat to the organic solid materials on preparing the suspeIIsion is not mixed with the hot steati~ condensate and the hot water expelled from the coal, so that a great portion of this excessive water i.s not heated what would be superfluols. Simultaneousl~vr, the water collected at the end of the process in a water collecti.ng con-tainer can be o~tained at a temperatl~re ].evel which is c~uf`l'icient for preheating the organic materials w}len preparing the suspensior,, Additional steam can he supplied un~er pressure when prepari.ng the sus,pensioIl for improving preheati.ng pri.or to l`eeding the sllspensi.on into the first succeeding dr~ing stage. ~lhe steam consumptlon c~m substantillly be redllced i.n vlew of the ~.i.gh temperatllres of the water to be recyc~.ed to t~e suxpensi.on.
Prefernbly, at least rl~ to ~() ,i of t}e water used for pre-paring the ~llspension is separlted bcforeor after entering the first succee(tlng drying strlge, noting that the rec~rcled or expelled water, respectively, can be separated from the sus-pension in a simple manner hy means of sieves, particularly slot sieves. ~`or thi.s pllrI)ose, an alltoclave maintained under steam pressure and pIovided with cascades of s].ot sieves can be usedO
The water to be by-passed relative to the remaining drying stages is in this case discharged from the pre-connected de-wateringr stage or from the first chamber o~ the sieve cascade or from the first chambers of the si.eve cascade located most adjacent to the char~ing opening of the autoclave, w~!ereby a stream of Orgmic materials already dewatered to a great extent is brought into contact with the steam r~upp~ into the autoclave.
The disc}large water can preferably be separated in a classi-fying stage into a portion depleted in solid Inaterials and into a portion enriched in solid materials, the portion depleted in solid materials being either discharged with interposition of an oxydi7ing equipment in which the orgl.nic matter is oxydi7ed by sup~lyirl~ ni.r or oxygen or bei.ng recycled fcr preparing the suspension, and the portion enriched in solid materials being recycled to the first dryi.ng stage. It is, however, also possible 11~2755 to introdl1ce the portion depleted in solid materials into a further purif~vring stage, pnr1;icll1nrly into an upstream-c].assi-fyer which results, however, in cooling down t~le process wzter which can be recycled for preparing the suspension.
~ he portion enriched i.n solid materials can be recycled into a drying stage, said rec~cling being preI'erably not only effected at the end of the dr~ing process into the stage in which the suspension is prepared, but being ~lso effected wit~
the by-passed portion of the process water and, in this case, the portion erlriched in solid materials beirLg recycled to the first succeeding stage. l'hat portion of the process water which is flowing Ollt of the last drying stage operated urder a pressure exceeding atmospheric pressure and which is enrichea in solid materials, can simply be introduced into the sl.udge or suspersion, respectively, below the licluid level t~lereof, whereby the sus-pension can more effectively be mixed and more intensely heated.
Introduction of the mentioned portion ol` process water is t~!Us conveniently ef.i'ected at the bottom end of the mixing receptacle used for preparing the suspension.
It is onl~ when the temperat~re of the portion of the process water recycled into the mixing receptac]e is insufficient for optimally preheating the organic solid m2terials that it is, according to the invention, proposed to additional]y heat the suspension wit~in the mixing receptacle by introducing steam which equ~lly is supplied in an advantageous manner below t~.e liquid level.
In -the following the invention is further illustrated with reference to the drawing showing various ernbodiments of a plant z75s for performing the process nccording to t~!e invention, 6aid embodi.ments il].ustrating further details essentia] for the invention.
In the drawi.ng ~ `igure 1 ~hows a J`irst embodiment of A plæ.nt for performing the process according to the invention, Figure ~ shows a modifi.ed embodilrlent of a plant corre-sponding to a ~lant as shown in ~'igure 1, ~ 'igure 3 shows a further modified embodiment of a plant for continuollsly drying fine-grained brown coal of high water content ~nd ~ `igure 4 shows a modil`ification of the embodimert shown in Figure 'I.
In ~'igure 1, reference numer~l 1 designates a bin for receivlng I`ine-grained brown coal having a grain si~.e of O.OQ1 to 20 r~m. Reference numeral ~ designates a suppl~r means designed as piston press by means of whic~: the coal grains or the coal dust, respectively, is pushed into a mixing receptacle 3. A
suspension of coal in hot water is produced within thi~ mixing receptacle 3 and supplied into an autoclave 5 by means of a pump 4. The mixing receptacle 3 represents the first drying stage and corQprises a stirrer 6. A conduit 7.is opening into this mixing recept~cle 3 and used for i.ntroducing into t~e mixing receptncle purified and cooled process water by means of a pump 8. A conduit 9 is equally opening i.nto the mixing receptac].e ~ clnd used for introducing hot process water con-taining coal. The co~l is supplied with a temperature of æpproxi.-mately 0 to ~0 ~ and the temperature of the suspension is _ 10 -275~

adjus-ted to approxima-tel~ 100 to 160 C b~r suppl~ing hot and cold water so that there is formed a saturated steam atmosphere.
C0~ generated and accumulated above the liquid level is vented via a lock 1~.
rrhe suspension of coal in hot water is supplied into the second drying ~tage formed of an autoclave 5 b~r means of a pump for exa~ple designed as centrifugal pump or a worm pump. This autoclave 5 comprises slot sieves11 through which excesE water is flowing off, the excess water being discharged via conduits 12.
The water di~scharged from the autoclave via the conduits 12 need not be heated subseqllently and optimal conditions are pro-vided for the action of the heated steam which is introduced into the alltoclave via a conduit 13 and nozzles 14. The coal particles moving downwardl~r within the autoclave come into con-tact with steam and the temperature within the alltoc~ave is raised to a value between ~00 and ~45 ~. ~eæ.t transmission by the conciensing steam atmosphere within the autocla~e 5 becomes thus essentiall~r more rapid than would be the case when using hot wate-~r. It is possible to use saturated steam as well as superheated steam but when using saturated steam it is advan-tageous to appl~r this steam with a pressure of 6 to 40 bar. The temperatllre and the pressure, respectivel~, of t~e steam is to a great extent dependent on the humidit~ content, the structure, the composition and the final water content ol` the coal and is also influenced by the mechanical strength of the coal and the intended use of the coal. ~team can be supplied via the nozzles 14 shown. It is however a]so possible to introduce the steam into " ll~Z'755 a fluidized bed of the coal. The hented and substantially dry coal is fa1ling onto the bottom 15 of the a~toclave and i9 by means of ~ transport scrdw 16 transferred into a third drying stage being designed as a centrifuge 17. Within this third drying stage the required temperature for final dr~ring is main-tained, separation of the water being efl`ected by means of the centrifugal forces so that again an optimum heat transmission from the steam to the coal is guaranteed. ~team is supplied into the centrifu~e via a connuit 1~, the process water being dis-charged via a conduit 1~ into a collecting container ~0 for waste water. '~'he centrifugal forces do not only enhance accelerated removal of water from the core of the coal particles but a]so assist the shrinking tendenc~ of the coal particles so that the danger that the coal again adsorbs alread~r removed humidit~r becomes reduced. rl'he coal particles becone plastic at the applied dryin~ tenperatures and beside a favourable shrinkage there is also observed an equalization of the grain size of the coal particles.
The stean supplied into the centrifuge 17 via the con-duit 18 convenientl~ enters the centrifuge adjacent the coal disch~rge ch~nnel 21 from where the dried coal is discharged via a lock 22 into anevaporating container ~3 opening into atmosphere at its upper portion. In this manner, the steam tem-perature is optimal]~r made use of.
The process water removed from the autoclave and containing, beside the water introduced with the suspension, steam condensate and water expelled from the coal is fed through a water 11~2 ~ 55 se~arator ~4, t~le portlon of the process water enric~ed in coal particles of extrenely fine grain size being introduced into the centrifuge. The process water is f`lowing l`rom the centri-fuge Vi.~l a conduit 19 into the collecting container ~0 for waste water, said collecting containcr ~0 bei.ng designed as settling tank in which the Wtste water is subjected to an upstream classi-fying. Yart of the waste water obtained is, after a correspond1ng resting time anci clarification, fed via a conduit ~5 into an oxydizing reactor ~6 in which organic matter, par-ticularly humic acids,are oxydized by introducing ox~ygen or air. ri`he required air or oxygen, respectively, can be introduced into t~e oxydation reactor ~6 via a conduit ~7. That portion of the process water, which is enriched in solid m~terials,is, via a con~uit ~, trans-ferred f.rom the collecting container ~0 for waste water into a dosing equi.pment ~ via which the hot water containing coal particles and coal dust is recrcled to t~Le first drying stage, i.e. the mixing receptacle 3, via the conduit 9.
rlhe coal supplied to the evaporati.ng container ~3 via the pressure lock ~, which can be designed as twi.n-lock, piston press or extruder, is su~lied by means of a conveyor means SO
to a fluidized bed dri.er 31 into which heated air is blown via a conduit ~. The dried coal is discharged at 33 and can be introduced into the stora~e container for drr fi,ne coal. The fi.nest COAl particles moved in upwlrd direction by the air in -the flllidized bed drier are separated in a cyclone~4- from which the soli(l materials are transferred into the disc~arge conduit 33 by means of a conve~ror screw 35. i`ine coal p-lr-ticles still con-tained in the air stream are separated in the dust filter 36 f`ollowlrlg the c~,rclone~4 and trallsferred into the disc~nrge conduit ~3 b~v~ means of a conve~ror screw ~7.
The process wnter purified wit~lln the ox~dation reactor is, via a pressure reducing vnlve 38 and a conduit 3~,intro-duced into n heat exchanger 4~ in which air ot` ambient tem-peratur i8 heated. The heated air is sllpplied into the fluidized bed drier 31 via a conduit.32. ~he condensate obtained in t~Le heat exch~nger is, by means of a pump 4.1, reeycled into the waste water conduit 4~ into which is introduced also the other portion of the process water flowing out ol` the oxydation reactor under pressùre. A pressure reducing va;ve 43 i.s a].so inter-connected into the waste water conduit 4~. 'l`he o~taired mixture of gas and steam is supplied to a heat exchanger 44 in whic~
boiler feed water for -the steam production equipment 45 is eated. ~art of the process water, which has been substantially eooled down within the hecLt exchanger 44,is, via the ~lmp ~ and the eonduit 7, again reeyeled into t~le nnixing reeeptacle under pressure. ~he excess portion of the proeess water flows into a sludge pond through a eonduit a6.
At t}ie lowernlost area of the autoclave 5 and above the liqui.d le~rel therein, there is again provided a loc~ 47 lor venting ~
In ~`igure ~, whi.ch shows a moctil'ied embociiment, there are used the same reference numerals as in ~'igure 1 for identieal constructiorLa] parts. Instead of the au-toc].nve 5 shown in Figure 1, a drying drum 4~ is used as the second dryin~ stage succeecting t~e mix~ng receptacle 3, a steam suppl~ concl~lit 13 ~e-~2~75S

ing connected 1;o this drying drum. 'l'he drying drum 4~ comprises a subs~anticll cylindrical, stationarily arranged sieve 49 and the coal su~perlsion supplied by p-lmp 4 and through the conduit 50 is fed in axlA]. direction ol` th.e dryi.ng drum b~ meanfi of a con-veyor screw ~1 dri.ven h~lr a motor 5c'. l'he sieve drllm can be pro-vlded with slot sieves, the process water being ~i~charged via conduits 53 from a plurality ol sections of the dr~ring equip-ment. 'l'he process water is flowing into a collectirlg container 54 within which the process water is further cl.arifi.ed and from which (,0~ is vented via a l.ock 55. At the lowermost area, the settled solid materia].s enter a conve~ror means 56 b~ which the solid materials are fed into a feed hopper 57 into which opens a]so the coa~ discharge conduit 5~ of` the drying drum arld which is also provided with a lock 5~ for venting ~. l'he coal con-tai.ned in the feed hopper 57 is transferred i.nto the centrifuge by the conve~.~or means 16 already described in connecti.on with , ~igure 1. rl'he process water coming from the col.lecting con-tainer 54 is, via a condui.t 60, immediately introduced into the conduit 1~ leading to the collecti.ng contai.ner ~0 for wafite water, hecause solid materials of this waste water have for the major ~art alread~y b~ihandled bvv the conveyor means 56 P.nd introduced into the centrifuge. In a],l. other respects the ~lant according to ~ligllre ~ corres~oncls to the plant according to ~`igure 1.
In the embodiment illllstrated bV~r l'ig~lre 3 the second drying stage sllcceeding the mixing receptacle 3 i~ designed as a centrifllge 61. rl`he hot sus~ension is supplied from the mixing ~1~2755 receptacle 3 and via a pump 4 to a slot sieve 6~, the portion enriched in solid materials being introduced into the centri-fuge by a conve~ror means 63. l'he conduit 13 f'or saturated steam or superheP~t,ed steam, res~ectively, is opening into t~le centrifuge closely to the discharge means 64 of t~!e centrifvge so that the heat energry is optimally utilized. The proceEs water flowing out oi` the centril'uge 61 is, via a conduit 65, again introduced into the condlli.t 19 leading to the co].~.ecting con-tairler ~ for waste water, a lock 66 for venting C0~ being inter-connected into this conduit 65. CO2 is also vented from the centri~uge 17 ~'orming the third drying stage via a lock 67. T~e process water passing through the slot sieves6~ is introduced into t~,e centriftlge ViP~ a conduit 6~ opening into the centrifuge close to the discharge end f'or process water, and thiæ f`or the purpose to utiliæe in the centrifuge 61 also f`ine-grained coal particles coming from said conduit 6~.
The remaining constructional parts of t~e plant shown in Figure 3 correspond to the plants shown in ~'igures 1 and 2.
In ~'igure 4, rel`erence numerals used in ~`igures 1 to 3 were retalned for equal constructional parts. 1 designates the bin for receiving fine grained brown coal or bituminous coal preferab1y having a gr~in size of O to ~O mm.. ~ designates the feed device designed as stamp press and pushing the coal grains and the coal dust, respectively, int;o the mixing receptacle 3.
Wit~lin this mixing receptacle 3, a susI)ension of coal i,n hot water ix prepared, said suspension being supplied to t~`e allto-clave ~ by means of the pump 4. The mixing receptacle 3 repre-sents the first dryi.ng stage and is provided wi,th. an agitating . - 16 - .

ll~Z~SS

device 6. Cooled arld puri.t`i.ed process water can be introdv.ced into the mixing rece~tacle ~ via the conduit 7 and by means of the pump ~. r~he conduit ~ is also opening into the mixing receptacle 3 and used for introducing hot process water con-taining coal sludge. 'l'he coal is supplied wi.th a temperature of about 0 to 40 (' and the temperature of the suspension is adjusted to approximately 100 to 160 C by surplying hot and cold water so that a saturated steam atmosphere is formed. l'he C2 accumulating above the liquid level is discharged via the lock 10.
rl1he suspension of coal in hot water is supplied into the autoclave ~ t orming the second drying stage by means of the pump 4, ~or example designed as cer.trifug-l pump or worm pump.
This autoclave 5 has , like the embo~imcnt according to ~`igure 1, slot sieves l1,by means o~' which excessive water can be se~arated, th.e water being discharged via conduits 1~. q'he water discharged from the autoclave via the conduits 1~ need not be ~eated later on and optimum conditions ~'or the action of steam are established which is introduced into the autoc].ave via the conduit 13 and nozzles 14. 'l`he coal particles moving down within this autoclave come into contact with this steam and the temperature within the autoclave is raised to ~00 to ~45 C. ~:eat transmission i8 ef'fected by the condensing steam atmosphere within the autoc].ave 5 at a substantially higher speed than when using hot wa-ter. ~atv.rPted steam as well as superheated steam can be used and it is of advantage to work with saturated steam under a pressure of' 6 to 40 bar. rl`he tem~eratllre and the pressure, respectively, of the -- 1rl ll~Z~5S

steam ls stron~ ,r dependent on t.~le watcr content, the str~lcture and the composition of the coal to be dried and on the final water content of the dried coal and is also influenced by the mechanica1 strength of t~le coal and its intended later use.
Steam can he sllpplied by means of the nozzles 14. The heated and substanti.ally dried coal, respectively, falls on the bottom 15 of the autoc1.ave and is transferred by means of' a conveyor screw 1 into a t,hi.rd drying stage which again is designed as ~entrif'~lge 17.
In this third drying stage the required final ~rying temperature is maintained arld the water is separated un~er the action of cen-tri~uga1 forces, so that again an optimum ~.eat transmlssion from the steam to the coal is guaranteed. The steam is supplied into the centrifuge via a condllit 1~ and the process water is discharged into a collectlng contalner ~ ~`or waste water vla a condult 1~. In addltion to t~le acce]erated removal of water from the core of the coal particles,the centrl~'ugal f'orces have also the efl`ect to enhance the shrinking tendency of' the coal particles so t~lat the danger that the coal particles again adsorb already removed humidity is reduced. At the drying temperatures used, the coal particles become plastic and in view of t~e coal particle shrinking Imder the action of the centri,fugal force, water contairled in the coal is pressea out and the grair. size of the coal part;icles is equalized.
The steam i.ntroduced into the centri~uge 17 via the con-duit 1~ conveniently enters the centrifuge ad3acent the coal discharge means 21 of the centrifuge, via which discharge means z~ss the dried coal is discharged via a lock 22 into an evaporating container 23 which has its upper portion open to atmosphere.
In this manner, the temperature of the steam is optimally utilized.
Whereas in the embodiment according to Figure 1 the process water discharged from the autoclave and containing in addition to the water contained in the suspension also steam condensate and water expelled from the coal is exclusively passed through a water separator 24 and the portion of the process water enriched in suspended coal of fine particle size is introduced into the centrifuge, a conduit 70 is connected to the both slot sieves located adjacent the charging end 69 and an amount of 75 to 90 percent of the water used for preparing the suspension is derived from this conduit 70 and not recycled to a further drying stage but by-passed past all drying stages. This co~duit 70 leads to a settling tank 71 designed as upstream classifyer in which the water is separated into a phase enriched in solid materials and into a phase depleted in solid materials. The phase enriched in solid materials--is fed to the bottom 15 of the autoclave 5 by means of a conveyor means 72 whereas the phase depleted in solid material is discharged via a conduit 73 with detour of all drying stages.
The process water emerging from the succeeding drying stages is flowing into the waste water collecting container 20 designed as clarifying tank via conduit 19, the waste water being subjected to an upstream classification within said collecting container.
Part of the waste water obtained is, in case there is an excess thereof, after a corresponding residence time for clarification ll~Z755 fed via the condtlit r~5 into the oxydation reactor ~6 wi.thin which b~ introducing oxygen or air the organic Matter is oxydiæed in an analogous mmner to that described in connection wi.th ~'igure 1. Air or oxygen, respectively, can be introduced into the oAc~,rdation reactor ~6 via the con~uit ~7. l'he porti.on of the process water,which is richer in solid material,is trans-ferred from the collecting container ~0 for waste water via the conduit ~ into a dosing device ~9 via which the hot process water containing coal of finest grain size is, via the conduit 9, recycled to the first dryi.ng stage, i.e. to the mixing receptacle 3 at the lower end thereof.
lhe coal transferred into the evaporating container 23 via the pressure lock ~2, which can be designed as a twi.n-lock, a piston press or an extruder, is fed by means of a conveying device 3~ into a fluidized bed drier -S1 into which heated æ.ir is blown via the conduit 32. lhe dried coal is discharged at 33 and can be transferred into a storage bin for dry iine coal.
'rhe coal particleshaving the finest particle size and having been carried i.n upward direction within the fluidized bed drier are separated within the cyclo~ 34 ~rom which the solid materials are led into the discharge conduit 33 by means of the conveying screw 35. Coal particles of extremely fine particle size sti.:ll contai.ned in the air stream nre separated in the dust fil~er 36 following the cyclo~34 and are transferred from the dust filter 36 into the discharge conduit 33 by means o~ a conveying screw 3l.
'rhe procesC3 water purified within the oxy~ation reactor :is, via a pressure reducing valve 3~ and a conduit 39, intro-r> O

duced into a heat exchanger 40 within which ambient air isheated, the heated air being introd~lced into the fl~lidized bed drier 31 via the condllit 32. The C02 formed during the oxydation reaction is discharged through the conduit 74. h pressure reducing valve ~3 is also interconnected into the waste water con~uit 4~. The mixture of gas and steam thus ob-tained is introduced into the heat exchanger 44 within which boiler feed water is heated f`or the steam generatin~ equipment 50.
A portion o~ the process water being cooled to a great extent behind the heat exchanger 44 is, via the p~p ~ and the con-duit 7, again supplied into the mixing receptacle 3 operated under pressure. ~l~he excess portion of the process water is flowing to the sludge pond via the conduit 46.
~ t the lowermost area of the autoclave 5 and above the liquid level therein, there is again provided a lock 47 lor discharging or venting CO~.
r~he phase depleted in solid materials and coming from the settling tank 71 is transferred into the sedimentation tank ~0 via the conduit 73, what, however, resu~ts in the drawback that the process water to be used for heating the suspension within the mi~ing receptAcle 3 is cooled down. l`heref`ore, a shut-off valve 75 is interGormected into this con~uit 73 to be in the position to shut off the conduit leading to the sedimentation container ~0. After having opened the closure valve 76, the phase depleted in solid materials can immediately be trans-ferred from the settling tank 71 into the oxydation reactor.
l'he slot sieves 11, which are arranged within the auto-clave 5 in cascade and in series, can, for the purppse of' 11~2~55 connecting the conduit 70 in a simple mnnrler be arranged such that a sieve portion comprising hollow-pyramidal. sieves is followed by a collecting case 77 comprising continuous walls the co71ecting case having perforations for the solid materials to pass therethrough either at i.ts cerltral area or at an area adjacent the ci.rcumfererlce of the alltoclave 5 in dependenae on the slot sieves having at their corresponding area inwardly inclined walls or outwardlr inc].ined wa~ls.
~ he steam generating equipment ~0 is tapped by a further conduit 7~ via which if required steam can be pressed into the mixing receptacle ~ to further preheat -the suspension. Such additional preheating is however only necessary if the temperatllre of the waste water introduced into the mi~ing receptacle ~ from the collecting container ~0 ~or waste water is insufIicierlt for optimally preheating the suspension.
rlhe process is particularly suitable for drying lignitic organic solid material such as brown coals.

Claims (23)

The embodiments of the invention in which an exclusive property or privilege is claimed are defined as follows:
1. A process for drying particulate organic solid material comprising: continuously suspendinq the organic materials having a maximum grain size of approximately 50 mm.
in water and heating to superatmospheric pressure in a first drying stage; subsequently passing the suspension through at least one succeeding drying stage to which steam is supplied to maintain or increase superatmospheric pressure; centri-fuging said suspension in one of said at least one succeeding drying stages; said at least one succeeding drying stage and all succeeding drying stages being supplied with steam to heat said organic solid material; continuously discharging a separated phase of said organic solid material from a last drying stage; releasing the pressure on said separated phase of solid material; and drying said separated phase of solid material by aeration.
2. The process of claim 1 wherein the suspension is passed over sieves prior to centrifuging.
3. The process of claim 2 wherein said sieves are slot sieves.
4. The process of claim 1, 2 or 3, wherein CO2 generated in individual drying stages is discharged or vented.
5. The process of claim 1 wherein the water is discharged into a settling container and classified into portions enriched in solid material and deplete in solid material, said portion of said discharged water enriched in solid material being recycled into a drying stage.
6. The process of claim 1 wherein said water is supplied to said first drying stage where said organic solid materials are suspended in an amount sufficient to heat said suspension to a temperature of at least 100°C.
7. The process of claim 6 wherein said water is supplied to said first drying stage from a supply thereof recycled from said process and enriched in said solid material.
8. The process of claim 1, 2 or 3 wherein the succeeding drying stages are operated at temperatures of at least 160°C.
9. The process of claim 5 wherein said portion of said discharged water deplete in solid material is introduced into oxydizing equipment within which organic matter is oxydized by supplying air or oxygen.
10. The process of claim 9 wherein the water leaving the oxydation equipment is pressure-released and the heat content of the water is utilized in heat exchangers for heating the boiler feed water and/or air.
11. The process of claim 10 wherein that portion of the water leaving the oxydizing equipment and being deplete in solid material is supplied to the first drying stage.
12. The process of claim l, 2 or 3 wherein steam pressures of at least 8 bar are utilized.
13. The process of claim 1, 2 or 3 wherein there is provided at least two drying stages in a steam atmosphere, steam condensate obtained and water expelled from the solid material being withdrawn from the process.
14. The process of claim 1, 2 or 3, wherein there are provided four drying stages, the second and the third drying stages being in a steam atmosphere, CO2 generated being extracted from at least the first and the second drying stage and the solid material being discharged from the fourth drying stage.
15. The process of claim 1 wherein the water used for preparing the suspension is, before or after entering the first succeeding drying stage, separated for a major part and either discharged with detour or circumvention of any further drying stages provided from the drying stages maintained under operating pressure and/or recycled at least partially into the first drying stage in which the suspension is prepared.
16. The process of claim 15 wherein 80 to 90 percent of the water used for preparing the suspension is separated immediately after entering the first succeeding drying stage.
17. The process of claim 15 wherein the recycled or discharged water is separated from the suspension by sieves.
18. The process of claim 17 wherein said sieves are slot sieves.
19. The process of claim 15, 16 or 17 wherein the suspension is passed in the first succeeding drying stage over a pre-dewatering means or a cascade of slot sieves arranged within an autoclave maintained under steam pressure, respectively, and in that the water separated is discharged from the cascades located nearest to the charging opening.
20. The process of claim 15 wherein the water is discharged from the first succeeding drying stage and separated in a classifying stage into a portion deplete in solid materials and into a portion enriched in solid materials, the portion deplete in solid materials being either dis-charged with interconnection of an oxydizing equipment within which organic matter is oxydized by air or oxygen supplied, or recycled for preparing the suspension and the phase enriched in solid materials being recycled with the first drying stage.
21. The process of claim 20, wherein the phase deplete in solid material is passed into a further purifying stage, particularly into an upstream-classifier.
22. The process of claim 15, 16 or 17 wherein CO2 generated within the oxydizing equipment is discharged.
23. The process of claim 1, 2 or 3, wherein the suspen-sion is heated and put under superatmospheric pressure by introducing steam under pressure prior to introducing the suspension into the first succeeding drying stage.
CA000362321A 1979-10-15 1980-10-14 Process for drying organic solid materials using steam Expired CA1142755A (en)

Priority Applications (4)

Application Number Priority Date Filing Date Title
ATA6711/79 1979-10-15
AT0671179A AT363905B (en) 1979-10-15 1979-10-15 METHOD FOR DRYING AND STRUCTURAL CONVERSION OF ORGANIC SOLIDS, E.g. BROWN COALS
AT0739779A AT369423B (en) 1979-11-20 1979-11-20 METHOD FOR DRYING AND STRUCTURAL CONVERSION OF ORGANIC SOLIDS, ESPECIALLY BROWN COALS
ATA7397/79 1979-11-20

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CA1142755A true CA1142755A (en) 1983-03-15

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AU (1) AU526002B2 (en)
CA (1) CA1142755A (en)
DE (1) DE3039012C2 (en)
GB (1) GB2065164B (en)
GR (1) GR70664B (en)
IN (1) IN152168B (en)
PL (1) PL131377B1 (en)

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* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
AT366089B (en) * 1980-01-21 1982-03-10 Voest Alpine Ag METHOD AND DEVICE FOR DRYING AND CONVERTING ORGANIC SOLIDS, IN PARTICULAR BROWN COALS
CH655782A5 (en) * 1981-07-03 1986-05-15 Escher Wyss Ag METHOD FOR DRYING A SOLID PARTICLE WET, MEANS FOR IMPLEMENTING AND APPLYING THE METHOD.
AT375387B (en) * 1982-11-03 1984-07-25 Voest Alpine Ag DEVICE FOR DRYING ORGANIC SOLIDS
AT380268B (en) * 1983-11-15 1986-05-12 Voest Alpine Ag METHOD FOR THE DRAINAGE OF PORTS BY CENTRIFUGING UNDER SATURDAM
DE3563978D1 (en) * 1984-03-21 1988-09-01 Voest Alpine Ag Drying installation for lignite with a high water content
WO2003018716A1 (en) * 2001-08-29 2003-03-06 Generation Technology Research Pty Ltd Coal dewatering system and method

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* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
DE713899C (en) * 1938-09-23 1941-11-17 Gustav Freimuth Process for the operation of the drying of fine coals, slimes u. Like. Serving slings
AT244292B (en) * 1963-03-29 1965-12-27 Georges Joffe Method and device for batch drying of colloidal substances, in particular lignite
AT260800B (en) * 1964-07-15 1968-03-25 Oesterr Alpine Montan Process for drying coal and apparatus for carrying out the process
AT260801B (en) * 1965-04-09 1968-03-25 Oesterr Alpine Montan Process for drying colloidal substances and devices for carrying out the process
AU430626B2 (en) * 1968-01-26 1972-11-26 Universityof Melbourne Separation of water from solid organic materials

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PL131377B1 (en) 1984-11-30
GB2065164A (en) 1981-06-24
DE3039012A1 (en) 1981-04-23
AU526002B2 (en) 1982-12-09
GB2065164B (en) 1984-04-04
GR70664B (en) 1982-12-06
IN152168B (en) 1983-11-05
DE3039012C2 (en) 1982-08-05
AU6329780A (en) 1981-04-30
PL227285A1 (en) 1981-06-19

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