. ~
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
-- 3 ---
2755
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
-- 4 --
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
Z755
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
-- 7 --
755
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-
- 14 -
~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
- 19 -
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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-
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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.
