Note: Descriptions are shown in the official language in which they were submitted.
103634~9
BACKGROUND 0~ THE INV~NTION
Fluld energy mllls of the con~ined vortex type
are well known and widely employed in certain industrle~
such as the plgment, co~metlc and plastic lndustries be-
csuse o~ thelr efflciency ~nd economy ln the grinding of
pulverulent ~olld~. A number Or early de6igns are de-
scribed ln considerable detail in U.S. Patent 2,032,827.
Most such fluid energy mills are varlation~ on
a ba~ic configuration of a generally clrcular chamber
enclosed by a pair of axial walls and a peripheral wall,
the axial length or helght of the chamber being ~ub-
stantially les~ than the diameter. At the periphery Or the
mill there is located at least one inlet for in~ectlng the
gaseous grinding fluid which furnishes the energy for
grinding the sollds, and one or more feed devices
~or lntroduclng the pulverulent solids to be ground. Pref-
erably several uniformly spaced apart lnlets for gaseous
grinding ~luld are provided around the circumference o~ the
mlll and they are oriented generally tangentially to the
chamber. An outlet coaxial to and ln direct communication
with the grinding chamber ls provided ~or discharge o~ the
ground ~ollds to a cyclone or bag rilter for collection.
Fluid energy mills of the foregoing type combine
both grlnding and clas~ification wlthln a slngle chamber.
A~ the gaseous grinding fluld i~ fed tangentially into the
perlphery of the chamber along with the solids to be ground
vortex i8 created ~hereby the particies are swept along
ln a splral path to be eventually discharged at the central
outlet. By proper ~election of operatlng condltlons, such
as rate And tangency Or fluid inJection, particles above
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a specific size can be kept within the mill until sufficient
attrition occurs, whereas other particles are allowed to
pass through.
Heretofore such fluid energy mills have not,
however, been satisfactorily operable except with pulverulent
solids which were in a relatively dry condition. Poor
grinding and even clogging of passages could occur if
excess liquid were present. This has been a disadvantage
in certain areas where the treatment of liquid-laden solids
such as slurries would be desirable. For example, in the
case of TiO2 pigments produced by the vapor phase oxida-
tion of TiCl4, the particles as formed are frequently
collected as a water slurry. The utilization then of a
fluid energy milling step, invariably needed to break up
particle agglomerates, has meant that it would first be
necessary to dry the particles, e.g., via a costly drying
operation.
The desirability of a fluid energy mill permitting
drying and grinding functions to be carried out simultaneously
will be apparent.
SUMMARY OF THE INVENTION
The present invention relates to a fluid energy
mill of the confined vortex type as described above but
with a feed device that enables it to be used for the
simultaneous drying and grinding of slurries of pulverulent
solids. More particularly there is used a slurry feed
device formed by
walls defining a generally rectilinear passageway
which opens into a peripheral region of the grinding
chamber,
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a slurry supply condult havlng an lnlet remote
.~rom the passageway and a dlscharge nozzle posltloned in
the pas6ageway for dlrectlng slurry along the passageway
.~ and toward the grinding cha~ber, the size of the dlscharge
nozzle belng 8mall relatlve to the surroundlng pas~ageway
to deflne an annular space therebetween,
means for supplylng gaseouR drying fluid of at
least ~onlc velocity to the annular space to thereby
envelop and atomize within the passageway slurry emerging
from the dlscharge nozzle, and
means ~or controlllng the temperature of the dis-
charge nozzle.
DETAILED DESCRIPTION OF THE DRAWINGS
The inYentlon will be further described with
reference to the drawin~s, not to scale and with the same
reference characters used to denote identical part~,
wherein:
Flgure 1 shows a side elevatlonal view, partly
in cross-~ectlon, of an apparatus of the inventlon, the - .
.. 20 slurry feed device being show.n generally as A,
- Figure 2 is a horizon~al Yiew, also partly in
cross-section, of the apparatus Or Flgure 1 taken normal ;: :
to the aX19 at the level of the inlet ~ets,
- Flgure 3 illustrates ln greater detall the slurry
~` reed devlce A, the view being a horlzontal cross-sectlonal
~: . vlew, and
. Figure 3a i8 a cross-sectlonal ~lew taken across
.- 3a-3a' Or Figure 3.
In Fig. 1 and Fig. 2, 1 ls a header ror ga~eous
30 - gr~ndlng ~luid and enclrcles peripheral ~al} 2 o~ generall~
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103~349
clrcul~r grlndin~ ~.hamber 3. Inlets 4, o~ whlch only rour
~re ~ho~n, interconnect the he~der and the grlnding chamber.
Axlal walls 5 and 6 of the chamber may be relatlvoly
parallel but in the preferred embodlment, a~ shown, come
clo~er to one another a~ the ch~mber axi~ i8 approached.
Circular di~charge port 7 and exhau~t duct 8 are axlally
located. Fluld from each inlet 4 enters the perlpheral
wall 2 generally tangentially of the chamber, l.e., at
an angle that is tangent to a circle about the center Or
the chamber which has a radius smaller than the radius Or
the chamber. A multipliclty of the~e inlets for gaseous
gr~nding fluid is advantageously u~ed, twelve belng con-
venient for a chamber of 27 inches diameter.
~ slurry feed device ~hown generally as A, and to
be described more fully hereinQfter ln connection with
~igure 3, ~erve~ to introduce }iquid-laden solids, preferablY
a solids slurry such as a TiO2 pigment ~lurry ln water, to
a peripheral region of the chamber through elongated pa~ago-
way 10, the latter being aligned nearly tangentially to
perlpheral wall 2 to facilitate flow of the solids into
the chamber vortex. Passageway 10 preferably opens ~to
the chamber directly through peripheral wall 2, as shown,
but it may alternatively open into the chamber through upper
. ~ axial wall 5 ln close proxlmity to peripheral wall 2. The
cyllndrical discharge opening rormed by dlscharge port 7, ln
con~unctlon with conical enclosure 9, ~orms a centri~ugal
separator into which the ground product settle~ to be col-
lected while the grindlng fluid ~lows out through e~haust
duct ~.
Rererring no~ to Figure 3 and to the details o~
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the slurry feed device A for introduclng ~nd drylng the
81urry, elone~ted pas8aeeway 10, throu~h whlch the ~ollds
ultimately pass into the grinding chamber, ls formed by
annular wall~ 21,22 which abut at flange~ 23,24, are held
! together by bolts 25, with an 0-ring gasket 26 in position
as shown. An extension of wall 22 forms housing 27 which
ie adapted to accommodate the entry of high velocity gaseou~
drying fluld, e.g., high pre~sure ~team suppl~ed vla pipe 28,
; which intersects passageway 10 at a rlght angle.
Communicating with pas~ageway 10 in axlal align-
ment with the relatively wider upstream portlon thereof
, . i8 a slurry ~upply conduit shown generally as 29 which i~
connected at its ~eed lnlet ~0 to a source of the ~lurry
i to be dried and ground. Conduit 29 is maintained in posi-
tlon against housing ?7 by means of bolts 33. 0-rings 35 are
ln contact wlth sh1m plate 34 to-ase~st ~n preven~ing le~k~
Or gaseous drying fluld.
Conduit 29 extends into houslng 27 and ls con~er-
gently tapered at its forward extremlty to form discharge
nozzle 36. The latter is centered within the wider portion
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of passageway 10 leaving a small annular space 37 between
pas~ageway lip 38 and discharge nozzle 36 for flow Or gaseous
drylng Muid so as to envelop the stream of slurry emerglng
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rom the dlscharge nozzle and passing into the narrower por-
- tlon of passageway 10.
By varying the thickness of shlm plate 34 the size
Or annular space 37 is varied.
' As shown more clearly in Figure 3a, slurry condult
~ 29 ls composed of inner cylindrical element 41 and outer
; 30 cylindrical element 42, the two being welded at each end.
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Hence, essentlally fully along the leneth Or corldult 29 i~
channel 39 for flow o~ heat exchange fluid, e.g., cold water,
therethrough. Elon~ated baffles 43 and 44 are welded to
cylinder 41 and extend nearly the entire length of ch~nnel 39.
m u~ the heat exchange fluld will for the most part enter at
threaded connectlon 45, traverse the length of conduit 29
through channel 39, return and finally exit at threaded con-
nectlon 46. It i8 especially desirable that the portlon of
condult 29 which is exposed to the high veloclty gaseous
drying fluid from pipe 28 be able to have lts temperature
appropriately controlled by the heat exchange fluid.
DESCRIPTION OF SPECIFIC EMBODIMENTS
.
Insofar as the grinding ~unction is concerned, the
operatlon of the fluld energy mill of the inventlon follows
that of ~lmllar devices of the prior art. In this respect
reference ls made to the arorementioned U.S. Patent 2,032,827
to Andrews and additionally to U.S. Patent 3,462~o86 to
Bertrand et al.
With respect to the improvement accordlng to the
present invention) gaseous drying fluid, preferably steam,
.
rlo~ing through pipe 28 at a relatlvely lo~ velocity and high
pressure, undergoes a marked increase in velocity, to at
least sonic velocity, as it emerges from what amounts to a
converging-diverglng nozzle at annular space 37 and comes in
conthct with slurry passing through discharge nozzle 36 at
a relatlvely lo~ velocity. Mass transfer and heat transfer
ln the reglon of the discharge nozzle are extremely rapid.
Deslrably, enough heat will be supplied by the gaseous
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103t;349
drylng rluld to permlt the temperature Or the resultlng mlx-
ture to remain above saturation temperature. The pulverulent
sollds will hence be at least surrace dry berore enterlng the
grinding chamber where they are subJected to the actlon of a
gaseous grlnding fluid, which like the gaseous drylng fluld
ls also preferably steam.
The envelope of gaseous drylng fluid about the
stream of slurry issuing from discharge nozzle 36 serves
not only in the drying ~unctlon but also in preventing a
buildup of solids along the wall~ of pa~æageway 10. Like-.
wlse, a flow of a cooling liquid such as chilled water
through channel ~9 of slurry supply conduit 29 aids in pre- ~ :
venting premature dryine of the slurry on the inner wall~
of the conduit or on discharge nozzle ~6. It ls par-
tlcularly important at start-up that the discharge nozzle
temperature not become excess~vely high before the slurry
~low i8 commenced in order that solid~ do not baka out
on the inner conduit wall.
While it is preferred to employ a multlplicity
Or inlets 4 f~r gaseous grinding fluid,as shown in Figures
: 1 and 2, it is also practical to omit them under certaln
. circumstances. For example where the grinding runction is
only of secondary importance as compared to the drying
~unction, the gaseous drying fluid supplied to chamber 3
vla passageway 10 can be adequate to serve a~ grlnding fluid
: a~ well.
Whlle the present inventlon is partlcularly de-
. ~crlbed wlth reference to the treatment of aqueou~ TiO2slurrie it will be apparent that it is also appllcable
:~ 30 to u~e wlth var~ous other materi~ls as well.
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; EXAMPLE
The materlal to be dried and ground ~s a slurry
ln water Or uncoated rutile TiO2 partlcles having an average
partlcle ~ize of about 0.22 mlcron. The solid~ content of
the slurry is 64~ by weight and its feed rate 18 6100
pounds per hour.
The fluid energy mill is that descrlbed ln
connection with the drawing~. The axial wall~ converge
from a height of ~-~ ~ inch at the perlphery to 2-1t4 inch
at the discharge port. The grlnding chamber is 27 ~nche~
in dlameter. There is a series of 12 tangential ring Jets
a~ inlets for ~low of 518qF., and 150 psig steam at the
rate o~ 3200 pound~ per hour into the grinding chamber.
The drying fluld is 800F, steam ~ed to a 2-7
inch lnternal diameter supply pipe at 450 pslg and at the
rate Or 8000 pounds per hours. The annular clearance
;5 ~urrounding the discharge nozzle of the slurry supply con-
~, duit ls 0.070 inch. ~he passageway is 1-7/8 inches in
diameter at the narro~est portion ~ust beyond the dis-
charge nozzle and expands to 2-7/8 inches in diameter; lts
~- length from the nozzle to the grinding chamber is 19-5/8
', inches.
~ he tem~erature of the steam di~charged from the
Brinding chamber is 338qF. The overall steam to pigmen~
r~tio is 7Ø
~he quality of the product i~ rated equivalent
O
to the same TiO2 dried separately and ground in a con-
- ventional m~nner. No pluggage o~ the slurry f~ed device
i8 encountered throughout an extended run.
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