CA1317267C - Roller mill - Google Patents
Roller millInfo
- Publication number
- CA1317267C CA1317267C CA000558634A CA558634A CA1317267C CA 1317267 C CA1317267 C CA 1317267C CA 000558634 A CA000558634 A CA 000558634A CA 558634 A CA558634 A CA 558634A CA 1317267 C CA1317267 C CA 1317267C
- Authority
- CA
- Canada
- Prior art keywords
- rotary
- classifier
- mill
- flow
- classifying
- 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 - Fee Related
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Classifications
-
- B—PERFORMING OPERATIONS; TRANSPORTING
- B02—CRUSHING, PULVERISING, OR DISINTEGRATING; PREPARATORY TREATMENT OF GRAIN FOR MILLING
- B02C—CRUSHING, PULVERISING, OR DISINTEGRATING IN GENERAL; MILLING GRAIN
- B02C23/00—Auxiliary methods or auxiliary devices or accessories specially adapted for crushing or disintegrating not provided for in preceding groups or not specially adapted to apparatus covered by a single preceding group
- B02C23/18—Adding fluid, other than for crushing or disintegrating by fluid energy
- B02C23/24—Passing gas through crushing or disintegrating zone
- B02C23/32—Passing gas through crushing or disintegrating zone with return of oversize material to crushing or disintegrating zone
-
- B—PERFORMING OPERATIONS; TRANSPORTING
- B02—CRUSHING, PULVERISING, OR DISINTEGRATING; PREPARATORY TREATMENT OF GRAIN FOR MILLING
- B02C—CRUSHING, PULVERISING, OR DISINTEGRATING IN GENERAL; MILLING GRAIN
- B02C15/00—Disintegrating by milling members in the form of rollers or balls co-operating with rings or discs
- B02C2015/002—Disintegrating by milling members in the form of rollers or balls co-operating with rings or discs combined with a classifier
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- Engineering & Computer Science (AREA)
- Food Science & Technology (AREA)
- Crushing And Grinding (AREA)
- Combined Means For Separation Of Solids (AREA)
Abstract
Abstract of the Disclosure The known roller mill associated with a rotary-type classifier is improved in a number of aspects. The improvements reside in that a downwardly convex flow-rectifying cone is disposed under the rotary type classi-fier and an upwardly convex slant plate for ejecting a sediment within the classifier is disposed above the flow-rectifying cone; that a baffle plate for hot air which covers a part of an upper side of a blow-up passageway of hot air provided along the outer circumferential portion of a turn table as spaced therefrom; or that the rotary classifier comprises a plurality of classifying blades disposed along generating lines of an inverse frusto-conical surface having a vertical axis and rotating about the axis to separate powder in a gas flow into fine powder and coarse powder, an angle formed between the classifying blade and a rotary radius is selected to be 30° to 60°, and an angle formed between the classifying blade and the rotary axis is selected to be 0° to 40°; either singly or in combination.
Description
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]
~ ' .
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.
~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 ~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 ~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 ~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.
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~ 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) 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-,~
. .
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 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 ~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 ~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.
,.. ..
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 ''..'~
.
~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]
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 ~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 ~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 ~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 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.
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]
~ ' .
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.
~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 ~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 ~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 ~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.
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~ 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) 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-,~
. .
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 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 ~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 ~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.
,.. ..
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 ''..'~
.
~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]
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 ~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 ~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 ~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 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.
Claims (2)
1. A roller mill comprising:
a table disposed within a mill main body and turned by a vertical shaft:
a plurality of rollers rotated as pressed against the upper surface of said table to crush material to be pulver-ized 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 upwardly convex slant plate for ejecting a sediment with the classifier, which plate is disposed above said flow rectifying cone;
baffle plates for diverting the gas flow inwardly and upwardly 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.
a table disposed within a mill main body and turned by a vertical shaft:
a plurality of rollers rotated as pressed against the upper surface of said table to crush material to be pulver-ized 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 upwardly convex slant plate for ejecting a sediment with the classifier, which plate is disposed above said flow rectifying cone;
baffle plates for diverting the gas flow inwardly and upwardly 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.
2. The roller mill according to claim 1, wherein rotary blades of the rotary classifier are inclined in their radial direction to a direction 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 O3 between each blade and the radial direction is 30 to 60°.
Applications Claiming Priority (6)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| JP62067907A JPH0773678B2 (en) | 1987-03-24 | 1987-03-24 | Roller mill with rotary classifier |
| JP62067908A JPH0757324B2 (en) | 1987-03-24 | 1987-03-24 | Roller mill with rotary classifier |
| JP62-67908 | 1987-03-24 | ||
| JP62-67907 | 1987-03-24 | ||
| JP17900587A JPS6422386A (en) | 1987-07-20 | 1987-07-20 | Rotary type sorter |
| JP62-179005 | 1987-07-20 |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1317267C true CA1317267C (en) | 1993-05-04 |
Family
ID=27299575
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA000558634A Expired - Fee Related CA1317267C (en) | 1987-03-24 | 1988-02-10 | Roller mill |
Country Status (7)
| Country | Link |
|---|---|
| EP (1) | EP0283682B1 (en) |
| CN (1) | CN1006852B (en) |
| AU (1) | AU585746B2 (en) |
| CA (1) | CA1317267C (en) |
| DE (1) | DE3863803D1 (en) |
| ES (1) | ES2024560B3 (en) |
| IN (1) | IN170412B (en) |
Cited By (2)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN102784703A (en) * | 2011-05-15 | 2012-11-21 | 盐城吉达环保设备有限公司 | Serially-connected grinding technology and equipment thereof |
| CN102784702A (en) * | 2011-05-15 | 2012-11-21 | 盐城吉达机械制造有限公司 | Parallelly-connected grinding technology and equipment thereof |
Families Citing this family (16)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| JPH07108387B2 (en) * | 1988-04-11 | 1995-11-22 | 三菱重工業株式会社 | Rotary separator for crusher |
| DE3839419A1 (en) * | 1988-11-22 | 1990-05-23 | Krupp Polysius Ag | DEVICE FOR FEEDING MATERIAL INTO A PLANT PART |
| JP2813361B2 (en) * | 1989-03-03 | 1998-10-22 | 三菱重工業株式会社 | Pulverized coal combustion method |
| CN2122687U (en) * | 1992-05-03 | 1992-11-25 | 武汉工业大学 | Centrifugal self-grinding mill with hammer moving along a vertical shaft |
| JP3207702B2 (en) * | 1995-04-04 | 2001-09-10 | 三菱重工業株式会社 | Rotary classifier for roller mill |
| WO2001019522A1 (en) * | 1999-09-14 | 2001-03-22 | F L Smidth & Co A/S | Method and apparatus for grinding of particulate material |
| DE102005040519B4 (en) * | 2005-08-26 | 2009-12-31 | Loesche Gmbh | Method and device for grinding hot and humid raw material |
| JP5905366B2 (en) | 2012-08-28 | 2016-04-20 | 三菱重工業株式会社 | Rotary classifier and vertical mill |
| JP6352162B2 (en) | 2014-11-28 | 2018-07-04 | 三菱日立パワーシステムズ株式会社 | Vertical roller mill |
| CN105013596B (en) * | 2015-07-14 | 2018-05-25 | 中国矿业大学 | Device and process for sorting difficult-to-grind mineral substances in cyclic load of coal mill |
| JP6629605B2 (en) * | 2016-01-27 | 2020-01-15 | 三菱日立パワーシステムズ株式会社 | Classifier, pulverizer and classifier and pulverized coal-fired boiler |
| CN106583003A (en) * | 2017-01-20 | 2017-04-26 | 重庆奇爽实业（集团）有限公司 | Improved pulverizer |
| JP6500066B2 (en) * | 2017-09-19 | 2019-04-10 | 三菱日立パワーシステムズ株式会社 | Biomass mill |
| CN108940558A (en) * | 2018-01-30 | 2018-12-07 | 上海意丰机电科技开发有限公司 | A kind of dynamic and static vane |
| CN109365063B (en) * | 2018-10-19 | 2023-09-08 | 四川亿欣新材料有限公司 | Multi-impeller vertical mill |
| CN111189985B (en) * | 2020-03-03 | 2022-05-31 | 上蔡县状元红食品质量检测服务有限公司 | Food nutrient content detection device |
Family Cites Families (6)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US2868462A (en) * | 1954-04-09 | 1959-01-13 | Combustion Eng | Pulverizing mill with novel outlet |
| FR1543548A (en) * | 1966-12-28 | 1968-10-25 | Combustion Eng | Rotating bowl mill |
| US4084754A (en) * | 1976-07-27 | 1978-04-18 | Loesche Hartzerkleinerungs-Und Zementmaschinen Gmbh & Co. Kg | Combined vane-rotor separator |
| DE8425837U1 (en) * | 1984-08-31 | 1984-11-22 | Krupp Polysius Ag, 4720 Beckum | Roller mill |
| US4759509A (en) * | 1985-08-15 | 1988-07-26 | Combustion Engineering, Inc. | Supermill journal spring system |
| IN166426B (en) * | 1986-02-24 | 1990-05-05 | Combustion Eng |
-
1988
- 1988-02-04 DE DE8888101623T patent/DE3863803D1/en not_active Expired - Lifetime
- 1988-02-04 ES ES88101623T patent/ES2024560B3/en not_active Expired - Lifetime
- 1988-02-04 EP EP88101623A patent/EP0283682B1/en not_active Expired - Lifetime
- 1988-02-10 CA CA000558634A patent/CA1317267C/en not_active Expired - Fee Related
- 1988-02-16 IN IN98/MAS/88A patent/IN170412B/en unknown
- 1988-03-22 CN CN88101496A patent/CN1006852B/en not_active Expired
- 1988-03-24 AU AU13588/88A patent/AU585746B2/en not_active Ceased
Cited By (2)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN102784703A (en) * | 2011-05-15 | 2012-11-21 | 盐城吉达环保设备有限公司 | Serially-connected grinding technology and equipment thereof |
| CN102784702A (en) * | 2011-05-15 | 2012-11-21 | 盐城吉达机械制造有限公司 | Parallelly-connected grinding technology and equipment thereof |
Also Published As
| Publication number | Publication date |
|---|---|
| DE3863803D1 (en) | 1991-08-29 |
| CN1006852B (en) | 1990-02-21 |
| CN88101496A (en) | 1988-10-05 |
| IN170412B (en) | 1992-03-21 |
| AU585746B2 (en) | 1989-06-22 |
| ES2024560B3 (en) | 1992-03-01 |
| EP0283682A3 (en) | 1989-04-05 |
| EP0283682A2 (en) | 1988-09-28 |
| AU1358888A (en) | 1988-09-22 |
| EP0283682B1 (en) | 1991-07-24 |
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