Note: Descriptions are shown in the official language in which they were submitted.
1 3172~7
_OLLER MILL
BACKGROUND OF THE INVENTION:
Field of the Invention:
The present invention relates in general to a
roller mill, and more particularly to a roller mill associ-
ated with a rotary-type classifier that is available for
pulverizing coal to be used in a pulverized coal fired
boiler, for pulverizing clinker to produce cement or for
similar purposes.
Description of the Prior Art:
At first, description will be made on one example
of the above-described roller mill associated with a rotary-
type classifier in the prior art with reference to Fig. 14.
The illustrated roller mill has such structure that within
a mill main body (1) is disposed a table (2) which is turned
by a vertical drive shaft (not shown), a plurality of
rollers (3) which are rotated while being pressed against
the upper surface of the table (2) to crush material (a)
to be pulverized are in opposition to the table (2), a rotary-
type classifier (6) is disposed above the table (2),thereby the material (a) to be pulverized such as lump coal
thrown into the mill through a feed pipe 18) is pressed on
I the turning table (2) by means of the respective rollers
(3) to crush it under a given load and eject it to the
outer circumference of the same table, hot air (bl
~ - 1 -
13~72~7
introduced through a hot-air inlet (4) at the below is fed
in association with the pulverized materi.al through a
blow-up section (5) opened along the entire outer circum-
ference of the table (2) into the mill main body on the
upper side of the table, thus the pulverized material is
sent to the rotary-type classifier (6) at the above by
the hot air, that is, the rising carrier gas, then the
above-men-tioned pulverized material is classified into
coarse powder and fine powder by means of rotary blades
(6a), the fine powder is derived through a discharge pipe~
(9) while the coarse powder is ejected to the outside of
the classifier and falls on the table ~2) to be crushed
again, and the bottom portion of the rotary-type classifier
is formed of a flat bottom p].ate (6b).
In the above-described roller mill, the coarse
powder ejected to the outside of the rotary-type classifier
is classified in weigh-t by the rising carrier gas blown up
- from the lower portion of the mill, and a principle of the
weight-classification is based on the Stokes' Law and
represented by the following formula:
~t = g (Ps ~ Pg) dp2/1~ ~g
whexe ~t: terminal sedimentation velocity of particles
with respect to a gas flow [cm/sec]
~g: rising velocity of a gas flow [cm/sec]
g: gravitational acceleration [cm/sec2]
-- 2
~ ' .
p5 density of solld; pg: density of gas
dp: par~icle diameter.
When the terminal sedimentation velocit~ ~t Of particles
with respect -to the gas flow is equal -to the rising velocity
~9 of the ~as flow, that is, ~t = ~g is fulfilled, the
particles appear to be still as viewed from the outside,
but if ~t ~ ~g is fulfilled, the particles appear to rise,
while if ~t > ~Ig is fulfilled, then the particle would
appear to descend.
The above-described roller mill associated with
a rotary-type classifier in the prior art involved -the
problems that a swirl would be generated under the fla-t
bottom plate of the rotary--type classifier, flow velocities
of air would become irregular at the inlet o-f the rotary
blades, hence a classification perEormance is greatly
deteriorated by the irregularity of the air flow veLocities
at the inlet oE the rotary blades because the rotary-type
classi:fier utilizes the mechanism of classifying into
coarse powder and fine powder on the basis of the ba:Lance
between a centriEugal force given by the rotation of the
ro-tary blades and a cen-tripetal force given to par-ticles
by an air flow, also fine powder would settle and pile on
the flat bottom plate, and i-f it continues to pile over
I a long period of time, in the case of pulverized coal, it
may cause autogeneous ignition or explosion.
-- 3
~3172~7
In addition, the above-desc:ribed roller mill in
the prior art involved an additional problem -that while
the coarse powder classified by the rotary blades of the
rotary-type classifier and ejected to the outside is ne-
cessitated to be made to fall on the table and to be crushedagain, due to the ~act tha-t the coarse powder consists of
particles raised by rising carrier gas and the rising
velocity of -the rising carrier gas is almost e~ual at every
location along a radial direction and a circumerential
direction on the transverse cross-section o the mill, the
above-men-tioned coarse powder would hardly all on the table,
as a result a powder density within the mill becomes high,
a pressure loss within the mill is increased, the interior
o~ the mill becomes a fluidized bed, resulting in a large
pressure variation, and this brings about large adverse
efects upon a pulverizing perormance.
Furthermore, in the rotary-type classiier pro-
vided in the roller mill in the prior art, despite of the
fact that a mount angle of the classiying blades i8 an
important factor largely ln~luencing upon a classiying
performance and hence there mus-t be an optimum range
the.reor, heretofore this mount angle was deter~ined
without relying upon any definite ground.
I
SUMMARY OF THE INVENTION:
I-t is thereore one object of the present
72~7
invention to provide an improved roller mlll associated
with a rotary-type classifier that is free from the above-
described shortcomings in the prior art~
A more specific object of the present invention
is to provide a roller mill associated with a rotary-type
classifier, in which a classifying performance and an
operational reliability are ~reatly improved, and a safety
is so enhanced that autogeneous igni-tion or explosion
within a classifier can be prevented.
Another object of the present invention is to
provide a roller mill associated with a rotary-type classi-
fier, in which a pressure loss within the mill and an
amplitude of a pressure variation are largely reduced, and
a pulverizing performance and an operational reliability
are greatly improved.
A still another object of the present invention
is to provide a roller mill associated with a rotary-type
classifier, in which a mount angle of the classifying
blades can be chosen at an optimum value, and thereby
classification of pulverized material into coarse powder
and fine powder can be achieved efficiently.
According to one feature of the present inven-
tion, there is prov1ded a roller mill associated with a
I rotary-type classifier, including a table disposed within
a mill main body and turned by a vertical drive shaft a
~ 5 -
`` ~3172~7
plurality of rollers rotated as pressed against the upper
surface of said table to crush ma-terial to be pulverized
in cooperation with said table; a blow-up section opened
along the entire outer circumference of said table into
the mill main body on the upper side of said table; a
rotary-type classifier disposed above said table for
classifying pulverized material in a rising carrier gas; a
downwardly convex flow-rectifying cone which is disposed
under said classifier; an up~ardly convex slant plate for
ejecting a sedimen-t with the classifier which plate is
disposed above said flow-rectifying cone; baffle pla-tes
for diverting the gas flow inwardly and outwardly above
each passageway of the blow-up section, said baffle plates
being formed between the outer periphery of the table and
the inner wall of the mill main body, spaced from said
passageways so as to cover a part of the upper side of the
blow-up passageways, being largely inclined and opened as
directed in the turning direction of the table and also
inclined and opened towards the center of the mill in
order to thereby form circumferentially spaced areas where
the velocity of the upwardly directed gas is small, said
areas being utilized as return passageways For making the
coarse powder, which is separated in the classifier,
return smoothly to the table.
.~
~ 3~72~7
In a preferred embodiment of the invention the
rotary blades of the rotary classifier are inclined in
their radial direction to a direc-tion opposite to that of
their rotation in order to make the coarse powder reach
quickly and surely to said return passageways, and wherein
the angle 03 between each blade and the radial direction
is 30 to 60.
In operation of the roller mill according to one
aspect of the present invention, the rising carrier gas
accompanied by the pulverized material flows into an inlet
of rotary blades after it has been rectified in flow by
the downwardly convex flow-rectifying cone disposed under
the rotary-type classifier, hence generation of a swirl
under the rotary-type classifier is eliminated, a flow
velocity of the rising carrier gas at the inlet of the
: rotary blades is made to be uniform, the classification of
pulverized material by means of the rotary blades becomes
smooth, then the fine powder settling within the rotary-
`~:
1~72~7
-type clas~ifier is made to slip down alony the upwardly
convex slant plate and ejected to the ou-tside of the
classifier, and it is mixed with the rising carrier gas and
then classi~ied again.
In operation of -the roller mill according to
another aspect of the present invention, hot air passed
through a blow-up passageway provided along the outer cir-
cumferential portion of the table within -the mill main
body becomes a rising carrier gas as accompanied by
pulverized material ejected to the outer circumference o
the table, a part of the rising carrier gas strikes against
the baffle plate and is diverted thereby, upon that diver-
sion coarse particles are primarily classified and caused
to fall on the table, and after the diversion a part having
a high rising velocity and a par-t having a low velocity are
produced in -the rising carrier gas within the mill main
body, then the part having a low rising velocity becomes
a falling passageway for the coarse powder classified by
the classifier, and the above-mentioned coarse powder would
Eall smoothly on the table jointly wi-th the coarse particles.
In operation of the roller mill according to
still another aspect of the present invention, owing to
the specifically defined attitude of the classifying blades
1 in the rotary-type classifier, separation between fine
powder and coarse pow~er can be carried ou-t efficiently,
~3172~
and -the rising carrier gas accompanied by the pulverized
material can smoo-thly flow into the space surrounded b~
the classifying blades.
Hence, according to the present invention,
various advan-tages are provided such that besides safety
o~ the roller mill, a classifying performance as well as
an operational reliability of the roller mill can be im-
proved, that a pulverizing efficiency can be greatly
enhanced, by largely reducing a pressure loss and an am-
plitude of pressure variation within the mill, and that a
separation eEficiency between fine powder and coarse powder
in the rotary-type classifier can be remarkably improved.
The above-mentioned and other objects, features
and advantages of the present inven-tion will become more
apparent by reference to the following description of
preferred embodiments of the present invention taken in
conjunction with the accompanying drawings.
BRIEF DESCRIPTION OF THE DRAWINGS:
In the accompanying drawings:
Fig. l is a schematic longi-tudinal aross--section
view showing a first preferred embodiment oE the present
invention;
I Fig- 2 is a diagram showing results of clasoi-
fication tests for difEeren-t inclination angles of a slant
- 25 plate;
~3~267
F'ig. 3 is a schematic longitudinal cross-section
view showing a second pre:Eerred embodimen-t of the present
invention;
Fig. 4 is a schematic transverse cross-section
view taken along line IV-IV in Fig. 3 as viewed in the
direction of arrows;
Fig~ 5 is an enlarged partial cross-s~ction view
taken along line V-V in Fig. 4 as viewed in the direction
of arrows;
Fig. 6 is a diagram showing distribution of
relative velocities of a rising air flow along a radial
d:irection of a mill;
Fig. 7 is a diagram showing distribution of
relative velocities of a rising air flow along the circum~
ferential direction of the mill;
Figs. 8(A) and 8(B) are, respectively, schematic
longitudinal cross-section views showing a third preferred
embodiment of the present invention;
Fig. 9 is a perspective view partly cut away of
a rotary-type classifier in the roller mill according to
the third preferred embodiment;
Fig. 10 is a schematic transverse cross-section
view taken along line X-X in Fig~ 8(A) as viewed in the
direction of arrows;
Figs. 11 through 13 are diagrams showing the
- 10 -
~3172~7
effects and advantages of the thi.rd preferred embodiment;
and
Fig~ 14 is a schematic longitudinal cross-section
view of a roller mill associated with a rotary-type classi-
fier in the prior art.
DESCRIPTION OF THE PREFERRED EMBODIMENTS:
A first preferred embodiment of the present
invention is illustrated in Fig. l, in which reference
numeral (l) designates a mill main body, numeral (2) des-
ignates a table, numeral (3) designates a roller, numeral (4) designates
an inlet of hot air, numeral (5) deisgnates a blow-up section of hot air,
numeral (6) designates a rotary-type classifyer, numeral
(8) designates a feed pipe of material (a) to be pulverized,
and numeral (9) designates a discharge cylinder of fine
powder. The construction of the roller mill associated
with a rotary-type classifier which forms a subjec-t matter .
of the present invention, is such that in a roller mill
including a table (2) disposed within a mill main body (l)
and turned by a vertical drive shaft (not shown), a plura:Lity
of rollers (3) rotated as pressed against the upper surface
of the table (2) to crush material (a) to be pulverized in
cooperation with the table (2), and a rotary-type classi-
I fier (6) disposed above the table for classifying pulverized
material in a rising carrier gas, a downwardly convex flow-
rectifying cone (ll) is disposed under the rotary-type
.
~3~267
classifier (6), and an upwardly convex slant pla-te ~12~ for
ejecting a sedimen-t within the classifier is disposed above
the flow-rectifying cone (11). The inclination angle of
the above-mentioned slant plate (12) i5 selected in corre-
spondence to a slip angle o~ the sedlment and preferablyto be a lit-tle steeper than the corresponding angle, the
slant plate (12~ rotates about the feed pipe (8), and the
flow-rectifying cone (ll) also can be made to llkewise
~ rotate.
Now description will be made on the operation of
the preferred embodiment oE the present invention having
the above-men-tioned construction~
The material (a) to be pulverized such as lump
coal charged through the feed pipe (8) is pressed by the
plurality of rollers (3) on the rotating table (2), thus
applied with a load to be crushed, and ejected to the outer
circumferential portion of the table (2), then hot air (b)
introduced through -the hot air inlet (~) a-t the below
passes through the blow-up section (5) and becomes a rising
carrier gas as accompanied by the ejected pulverized ma-
terial, this rising carrier gas rises through -the inner
space of the mill main body (l) above the table (2), flows
into an inlet ~ection of rotary blade ~6a) after it has
I been rectified in flow by the downwardly convex rectifying
cone (ll), and since generation of a swirl under the
~ 3 ~ 7 i~d ~ 7
ro-tary-type classifier (6) is almost ellminated by the
rectifying cone (ll) and flow velocities of -the r,ising
carrier gas at the inlet section of the rotary bl,ades (6a)
are made to be uniform, the pulverized ma-terial in t~e
rising carrier gas can be classiEied smoothly and effi-
ciently by the rotary blades (6a), and thereby a classify-
ing performance into coarse powder and fine powder can be
greatly enhanced.
The classified fine powder is derived through
the discharge cylinder (9) jointly wi-th the carrier gas,
while the coarse powder is ejected to the outside of the
classifier by the rotary blades (6a) and falls on the table
(2), and then it is crushed again.
It is inevitable that a part of coarse powder
flows into the inside of -the rotary blades (6a), that is,
-to within the ro-tary--type classifi.er (6) jointly with fine
powder, and so, within the rotary-type classifier (6) a
sediment of fine powder or -the lil~e is liable -to be produced.
However, this sediment woul.d slip down to the circumference
due to existence oE the upwardly convex slant plate (12),
thus it would be ejected -to the ou-tside of the classifier
within the mill main body (1) and mixed with the rising
carrier gas to be reclassified, and -thereby accurnulation
! of a sediment within -the classifier can be prevented.
Regarding the inclination angle o~ the slant
- 13 -
~3~267
pla-te (12), that is, the slip angle i.n the case of coal,
the 51ip angle of coal is dif-ferent depending upon a
variety of coal as indica-ted in l'able-1 below, for instance,
in the case of Chinese coal (E) having a slip angle of 25.4
degrees, it is preferable to select the inclination angle
of the slant plate ~12) to be about 30~, and if -the slant
plate (12) is rotated, slip-down of the sediment becomes
smooth.
Results of tests of a classifying performance for
different inclination angles l of the slant plate (12) are
shown in Fig. 2 (in this example, evaluation is made on
the basis of an amount of particles having a particle di-
ameter of 149 ~m or larger which Eorm coarse granular
material in the product coal), and according to -the test
results in Fig. 2, the above-mentioned inclination angle l
with respect to the horizontal plane provides an optimum
result at 30 - 60 degrees. If the inclination angle l
becomes larger than 60 degrees, though degradation of a
classifying performance is relatively small, the vertical
length of the slant plate ~12) would become remarkably
large and hence would be unfavorable in view of arrangemen-t
within the mlll, and so, the improvement of the classifying
performance is supplemented by rotation of the slant plate
(12).
In Table-2 below are shown results of tests for
- 14 -
~317267
a classifying performance in the case of -the mill in the
prior art and in the case of the mill according to the pre-
sen-t invention in terms of grain size distributions of the
product coal (pulverized coal at the outlet of the mill).
In the case of the mill according to the present invention,
for the same rotational speed o~ the classifier, the amount
of particles having a grain size 74 ~m or smaller is more
by about 2~, and the amount o~ coarse particles having a
grain size of 149 ~m or larger which adversely affect the
combustibility i.s reduced to less than one-half. In this
case, the rotational speed of the classifier can be made
to be lower by about 20%, and this is an effect brought
about by equalization of an air velocity distribution a-t
the inlet of the classifier caused by the flow-rectifying
cone (11) and ejection and reclassification of a sediment
caused by the slant pla-te (12).
Accumulation of fine powder or -the like at the
lower portion within the classifier becomes almost un-
detectable, and i-t has been confirmad that the mill can be
operated safely without the fear of autogeneous firing or
explosion caused by accumulation of Eine powder or the like
at all.
~ ! ~
,
- 15 -
~3~ 7267
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-- 16 --
~ 3 ~ 7
A second preferred embodiment of -the present
invention is illustrated in Figs. 3 -to 5, in which re:Eerence
numeral (1) designates a mill main body, numeral (2) des
ignates a table that is turned by a vertical drive shaft
(not shown), numeral (3) designates rollers rotated, as
pressed against the upper surface of the table (2), numeral
(4) designates an inlet of hot air, numeral (8) designates
a feed plpe of material to be pulverized, numera:L (9) des-
ignates a discharge cylinder, numeral (5) designates a
blow-up passageway of hot air disposed locally on -the outer
circumferen-tial portion of the table (2), and numeral (6)
designates a rotary type classifier disposed in the upper
portion within -the mill main body (1). The construction
is such that the mill includes a table (2) disposed within
the mill main body (1) and a plurality of rollers (3)
rotated as pressed against the upper sur~ace of the table
(2) to crush material to be pulverized, a blow-up passage-
way (5) of hot air is disposed on the outer circumferential
portion of the table (2), and a baEEle pla-te (20) for hot
air covering a part of the upper side of the blow-up pass-
ageway (5) as spaced therefrom is disposed above the blow~
up passageway (5).
In more particular, the above-mentioned blow-up
! passageways (5) are disposed in multi.ple (three in the
illustrated case) between hot air shut-off plates (Zl)
- 17 -
13172~7
provided along the outer circumferential portion o the
table (2), as spaced from each other in the circumferential
direction as shown in Fig. 4, and the arrangement is such
that hot air (b) may be made to pass towards the base si~e o~ a
baffle plate (20) by means of a plurality of guide plates
(15a) disposed in parallel to each other. As shown in
Figs. 4 and 5, the above-described baffle plates (20) are
disposed above the respective blow-up passageways (5) as
spaced therefrom so as to cover a part of the upper side of
the blow-up passageways (5), they are largely inclined and
opened as directed in the turning direction of the table
(2) (in the direction by an arrow) and also inclined and
opened towards the center of the mill, hot air passed through
the respective blow-up passageways (5) becomes a rising
carrier gas accompanied by the pulverized material ejected
to the outer circumference of the table (2), a part of the
above-mentioned rising carrier gas striXes against the lower
surface of the baffle plate (20) and is diverted thereby,
and then it flows out through the above-mentioned openings
and becomes a rising carrier gas within the mill main body~
In the above-described rotary-type classifier (6),
an upwardly convex slant plate (12) is disposed at the
bottom end of rotary blades (6a), a downwardly convex flow-
rectifying cone (11) is provided on the downside of -the
slant plate (12), hence the slant plate (12) and the flow-
- 18 -
,~
. .
1 3 ~ 7
rectifylng cone (11) ro-ta-te toge-ther, and thereby fine
powder or -the like (possibly including coarse powder)
deposited on the inside of the ro-tary blades (6a) are made
to slip down to the circumferen-tial portion by the slant
plate (12).
The second prefsrred embodiment of the p~esent
invention is constructed as described above, and now de-
scription will be made on the operation of the second
preferred embodiment.
Material (a) to be pulverized such as lump coal
charged through the Eeed pipe (8) is pressed by a plurality
of rollers (3) on the turning table (2), applied with a
load, crushed and then ejected to the outer circumference
of the table (2). Hot air (b) introduced through the hot
air inlet (4) at the below, is passed through the respective
blow-up passageways (5), and becomes a rising carrier gas
(b') as accompanied by crushed material Gf the ma-terial (a)
to be pulverized that is ejected to the outer circumfer-
ential portion of the table (2), then a part of -the rising
carrier gas (b') strikes against the lower surface of the
baffle plate (20) and is diverted thereby, and it passes
through the openings on the side of the circumferential
direction and on the side of the center of the mill and
! rises within the mill main body:. When the above-mentioned
carrier gas (b') strikes against the lower surface of the
- 19 -
1 ~17~67
baffle plate (20), coarse particles contai.ned in the pul-
verized material are greatly diverted and fall on the table
(2), and thereby primary classification is carried out.
Since the respective por-tions o~ the rising
carrier gas (b') are partly diverted by the corresponding
baffle plates (20), a high rising velocity portion and a
low rising velocity portion of the rising carrier gas are
produced wi-thin the mill main body (1) on the upper side
of the baffle plates (20). The rising velocity of the ris~
ing carrier gas is raised on -the side of the center of the
mill (X), whereas it is lowered on the side of the circum-
ference of the mill (Y) as shown in Fig. 6, and also as
shown in Fig. 7 high rising velocity portions and low
rising velocity portions are produced alternat.ely along
lS the circumferential direction.
The rising carrier gas accompanied by the pul-
verized material rises within the mill main body, and is
passed to the i.nside of the rotary blades (6a) after it
has been rectified in flow by the flow-rectifying cone (11~,
the pulverized material in the rising carrier ~as is
classified by the rotary blades (6a) into coarse powder and
fine powder, and the fine powder is derived through the
discharge cylinder t9), while the coarse powder is e~ected
! to the outside of the rotary-type classifier (6) by the
action of the rotary blades (6a), then alls on the table
- 20 -
~317~7
(2) and is crushed again.
Since a high rising velocity portion and a low
rising velocity portion as described above are produced in
the rising carrier gas within the mill main body, the above-
mentioned coarse powder would fall at the portion havinga relatively low rising velocity, and thus a plurality of
falling passageways are formed.
The above-mentioned falling passageways for coarse
powder are partly formed in the rising carrier gas, hence
they do not cause any special hindrance to the rise of the
pulverized material caused by the high velocity portion, a
pressure loss is greatly reduced, and the falling of coarse
powder onto the table becomes smooth.
The upper surfaces of the hot air shut-off plate
(21) and the respective baffle plates (20) are ~ormed in
slant surfaces having an inclination angle corresponding
to a slip angle of the coarse powder in question but a
little larger than -the latter. For instance, in the case
of coal a slip angle of at least 16 - 47 degrees is neces-
sitated as shown in Table-l above though it may be different
depending upon varieties of coal~ Hence it is preferable
to select the inclination angle on -the upper side of the
hot air shut-off plate and the baffle plates to be equal to
the slip angle in the table plus about lO degrees, then the
coarse powder, that is, the material to be pulverized on the
hot air shut-off plate (21) and the respective baffle plates ~20) would
- 21 -
~3172~7
slip and fall onto the table (2) and would be crushed.
Although a most part of the coarse powder is
separated and falls on the table ~2) as described above, a :
part of the coarse powder would flow into the rotary~type
classifier (6). On the inside of the rotary blades (6a),
sedimentation of fine powder as well as coarse powder would
occur, the sediment is made to slip and fall by the slant
plate (12) and mixed with the rising carrier gas on the
outside to be reclassified, and coarse powder would fall on
the table (2) simila~y to the above-described primary
classification.
As a result of comparative tests conducted for
System-A in which while a hot air blow-up passageway is
- provided along the entire ~ength of the outer circumference
of the table (2), a slant plate (12) is provided in the
rotary-type classifier but a baffle plate (20) is not
provided, and System-B according to the above-described
second preferred embodiment of the present invention, it
was proved that a mill pressure loss and an amplitude of
pressure variati.on are as indicated in Table-3 below,
thus in the case of System-B embodying the present inven-
tion, a favorable result was obtained in that a pressure
loss was reduced by about 30% and an amplitude of pressure
I variation was reduced to about one-half.
- 22 -
,.. ..
13~72~7
Table-3
System A ¦ (present ln ention)
Mlll 49Omm H20 35Omm H20
Pressure
variation 1 ~20mm H20 +lOmm H20
amplitude ,
Now a third preferred embodi~ent of the present
invention will be described with reference to Figs. 8 to lO.
This preEerred embodiment provides further improvements on
the first preferred embodiment shown in Fig. l as illustrated
in Fig. 8(A) and on the second preferred embodiment shown
in Figs. 3 to 5 as illustrated in Fig. 8(B) in that a
classifying efficiency of the classifying blades in -the
rotary-type classifier is optimized, as will be described
in the following. Hence, thus preferred embodiment includes
component parts similar to those used in the first and
second preEerred embodiments, and the equivalent component
parts are given like reference numerals.
In Figs. 8 to 10, reference numeral (10~ des-
ignates an upper support plate for classifying blades (6a),
a plurality of classifying blades (6a) are disposed along
! generating lines of an inverse frusto-conical surface
having a vertical axis, and supported at their upper and
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.
~3~72~7
lower ends by the upper support plate (10) and a downwardly
convex flow-rectiying cone (11), and they are adapted -to
be rotated about a feed pipe ~8) that is disposed along the
vertical axis of the above-mentioned inverse frusto-conical
surface. In the illustrated embodimen-t, an angle 03 (See
Fig. lO) formed between the classifying blade (6a) and a
rotary radius is selected to be 30 to 60, and an angle 2
(See Fig. 8) formed between the classifying blade (6a) and
the rotary axis is selected to be 0 to 40. A principle
of classification into coarse powder and ine powder by
rotation of the classifying blades (6a) is based on the
following two effects:
(A) Balance_between the forces acting upon -the
particles having entered into the classifying
blades:
As shown in Fig. 10, upon the particles within
the blades ac-t a fluid resistance R directed in the centri-
petal direction caused by an air 10w and a centrifugal
force F caused by the rotary motion, and the respective
Z0 forces are represented by the following formulae:
R = 3~d~Vl
6 (Pl P2) r
! where d: particle diameter [cm]
~: viscosity of gas [poise]
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11 3~7267
V1: velocity in the centripetal ~irection of
gas [cm/sec]
V2: circumferential velocity of blades [cm/sec]
Pl, P2: densities of particles and gas ~g/cm3]
More particularly, when the classifier is operated
under a fixed condition, coarse particles for which F ~ R
is fulfilled are ejected to the outside of the classifier,
while fine particles for which F < R is fulfilled flow to
the inside of the classifier, and thereby the pulverized
material can be classified into coarse particles and fine
particles.
(B) Direction o:E reflection (~) after the particles
have struck against the blades:
In Fig. 10 is also shown the state oE the particle
striking against the bladeu When the direction of reflec-
tion (a) after -the particles have struck against the blades
is directed more outwards than a tangential line, the
particles are liable to be ejected to the outside of the
classifier, whereas when the direction (a) is directed
inwards, the particles are apt to flow into the classifier.
It has been known that when a gas flow enters a space
between the classifying blades, swirl flows are generated,
then fine particles make movement close to the swirl flow,
but coarse particles come out of the swirl Elow and make
movement close to straight movement. Consequently, the
~; ~ - 25 -
1317~67
direc-tion of reflection af-ter the fine particles have struck
against the blades is apt to be direc-ted inwards, whereas
-that of the coarse particles is apt to be directed outwards,
and -thereby classification into fine particles and coarse
particles can be effected.
Here, le-t us consider about the inclination angle
(mount angle) of the classifying blade (6a). In Fig. lO
representing an inclination angle of the classifying blade
(6a) with respect to the direction of the rotary radius r
by ~3, as this inclination angle ~3 becomes large, a
probability of the particles having struck against the
classifying blades (6a) jumping ou-t to the outside is
increased, and so, fine particles passing throuyh the space
between the classifying blades (6a) and coming to the
interior would become fine, in other words, an average
particle diameter of the classi-fied product would become
ine. In this case, the amount of the product is reduced.
If the inclination angle ~3 becomes small, inverse ph0no-
mena would ar:ise.
In addition, if an inclination angle of the
classifying blade (6a) with respect to the rotary (vertical)
axis is represented by ~2 as seen in Fig. 8, a magnitude of
thls inclination angle ~2 would seriously affect the problem
whether or not generation of swirls in the proximity of or
inside of the class~fyin0 blades (6a)~ is little and a
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~3~7~67
carrier gas can smoothly flow into the classifying blades.
In -the third preferred embodiment Oe the present
invention, for the purpose oE insuring a stable classifying
performance, as described above in F'ig. 10 the angle ~3
formed between the classifying blade (6a) and the rotary
radius r is selected to be 30 to 60. In addition, in
~ig. 8 the angle 2 formed between the classifying blade
t6a) and the rotary axis (the ver-tical direc-tion) is
selected to be o D to 40.
Fig. 11 shows a relation between the angle ~3 and
a wearing rate of the classifying blade. According to this
diagram, for the angle 03 in the proximity of 25 the
wearing rate becomes maximum, and it is reduced over the
range of the angle 03 from 30 to 60. ~ig. 12 shows rela-
tions between the angle 03 and an amount of product as well
as an average particle diameter in the product. As the
angle 03 becomes large, an amount of product is reduced in
accordance with the angle, and an average particle diameter
also becomes small. However, in the range of 45 ' 15,
a separating effect would ac-t grea-tly, and a product having
a small average particle diameter can be obtained. In view
of the above-descxibed relations, it can be said that a
region of the angle 03 where operation of a mill having
balanced values for a wearing rate of classifying blades,
an amount of product and an average partLcle diameter can
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~317~7
be achieved, is 45 ~ 15.
On the other hand, ~ig. 13 shows a relation
between the angle ~z and an average particle diame-ter in
a product. For a given specific gas flow rate (practical
gas flow rate/reference gas flow rate) of a carrier gas
containing powder, there must be an optimum inclination
angle ~2 for which an amount of coarse particles mixed in
fine particles after classification (practical amount/
reference amount) becomes minimum, and in the range adapted
for practical use, an average particle diameter becomes
minimum in the range about 20 ~ 20, that is, in the range
of 0 to 40, and the separating effect becomes large.
The roller mill according to the presen-t inven-
tion is constructed as described above, hence a rising
carrier gas accompanied by pulverized material enters in-to
an lnlet of the rotary blades after it has been rectified
in flow by the downwardly convex ~low-rectifying cone, thus
generation of swirls under the rotary-type classifier is
eliminated, flow velocities of a rising carrier gas at the
inlet o~ the rotary blades are made to be uniform, classi-
fication of materials to be pulverized by the rotary blades
becomes smooth, an efficiency of classificat1on is enhanced,
also a sediment of fine powder or the like within the
classifier is made to slip and fall due to the slant plate,
then it is mixed with the rising carrier~gas on the outside
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~3~7267
of -the classifier to be reclassified, and thereby advantages
are provided such tha-t a classifying performance and an
operational reliability are remarlcably improved, and a
safety i9 enhanced in such manner that for ins-tance, au-to-
S geneous firing or explosion wi-thin a classi~ier can be
prevented.
In addition, according to another aspec-t of the
present invention, hot air passed through a blow-up passage-
way provided along an outer circumferential portion of a
table within a mill main body becomes a rising carrier gas
as accompanied by pulverized ma-terial ejected to the outer
circumference of the table, a part of the rising carrier
gas strikes against a baffle pla-te and is diver-ted thereby.
Upon -this diversi~n coarse par-ticles are primarily classi-
fied and made to fall on the table. After the above-
mentioned diversion high rising veloci-ty por-tions and low
rising velocity portions are produced in the rising carrier
gas within the mill main body, the low rising veloci-ty
portions become falling passageways for eoarse powder
elassified by the elassifier. Henee the above-mentioned
eoarse powder can fall smoothly onto the table jointly
with the above-described coarse particles, -thus a falling
performance of coarse powder or the like ean be remarkably
enhaneed, a pressure loss and an amplitude of pressure
variations within the mill are greatly reduced, and a
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72~
pu.lverizing performance and an operational reliabili-ty are
greatly improved.
Furthermore, according -to still another aspect
of -the present invention, owing to the fact -tha-t an angle
formed between a classifying blade of a rotary classifier
in a roller mill and a ro-tary radius is selected to be 30
to 60 and an angle formed between the same classifying
blade and a rotary axis to be 0 to 40, a roller mill
incorporating a rotary-type classifier having the optimum
configuration can be provided, and -thereby classification
into fine powder and coarse powder can be carried out
efficiently.
While a principle of the present invention has
been described above in connection to preferred embodiments
of the invention, it is a matter of course tha-t many
apparently widely different embodiments of -the present
invention could be made withou-t departing -from the spirit
o the present invention.
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