Classifying – separating – and assorting solids – Fluid suspension – Gaseous
Patent
1994-09-03
1996-07-09
Bollinger, David H.
Classifying, separating, and assorting solids
Fluid suspension
Gaseous
B04B 512
Patent
active
055336299
DESCRIPTION:
BRIEF SUMMARY
TECHNICAL FIELD
This invention relates to a vortex pneumatic classifier to be used for the object of classifying granular or powdered raw material, such as cement, calcium carbonate, ceramics, etc.
BACKGROUND ART
A conventional vortex pneumatic classifier disperses with air flow particulate raw material, for example, granular or powdered material such as limestone dust, classifies the said granular or powdered material into coarse powder and fine powder employing the balance between centrifugal force and drag force, and at the same time, discharges the said fine powder to the exterior of the machine, which then becomes product. (See Japanese Patent Publication No. 57-24189.)
As is generally known, in the event that the theoretical classifying particle diameter Dp(th) [m] is where the particle Reynolds number Rep=Dp(th) Vr .rho.f/.mu.<2, it can be obtained by the general formula described below. ##EQU1##
In this general formula, Vt indicates the peripheral speed (m/s) of the tip of the vortex flow adjusting vanes, .mu. indicates the viscosity coefficient of the air (Pa.S), D indicates the rotor diameter (m), Vr indicates the speed of the inwardly flowing air (m/s) at the tip of the vortex flow adjusting vanes, and .rho.p indicates the density of the air.
However, upon comparison of the theoretical classifying particle diameter Dp(th) obtained from the said general formula and the classifying particle diameter obtained from actual classifying Dp(obs), it has been found that the Following relationship exists between the two, and these two do not necessarily agree. becomes, the larger the classifying particle diameter actually obtained Dp(obs) becomes as compared to the theoretical classifying particle diameter Dp(th).
This inventor has found the following to be true, upon studying the cause of the said relationship between the particule diameter Dp(th) and the particule diameter Dp(obs).
As shown in FIG. 6, the tangential direction flow speed distribution of the flow within the vortex-type pneumatic classifier which is provided with guide vanes A8 and vortex flow adjusting vanes (rotor blades) A6 which are opposed across the classifying chamber A7 is described as W in FIG. 6. The classifying particle diameter Dp is determined by the balance between; centrifugal forces F.sub.cA and F.sub.cB which are dependent on tangential direction flow speeds V.sub.tA and V.sub.tB, and drag forces F.sub.dA and F.sub.dB which are dependent on inwardly flowing air speed.
This classifying particle diameter Dp gradually becomes smaller upon the radius which extends from the guide vane part A to the vortex adjusting vane tip part B, and becomes larger again on the inside of the vortex adjusting vane tip.
Therefore, of the classifying material placed between the guide vanes A8 and the vortex flow adjusting vanes A6, the particles which are larger than the classifying particle diameter at point B are recovered to the coarse powder side, while the particles which are smaller than this are recovered to the fine powder side. That is to say that the classifying particle diameter for this machine is the classifying particle diameter D.sub.pB at point B.
As mentioned above, the classifying particle diameter D.sub.pB is determined by the tangential direction flow speed V.sub.tB and inwardly flowing air speed at this point, the actual tangential direction flow speed V.sub.tB does not necessarily agree with the rotor peripheral speed, but has a slight delay. That is to say, the flow speed of the tangential direction flow speed distribution W at point B is slower than the rotor peripheral speed R indicated by the broken line.
On the other hand. V.sub.tB uses the rotor peripheral speed R for calculation of the theoretical classifying particle diameter Dp(th). This is the reason for the difference between the theoretical classifying particle diameter Dp(th) and the actual classifying particle diameter Dp(obs). Especially, in instances where the rotor peripheral speed is great, the difference between the tangential direction flow speed
REFERENCES:
patent: 4689141 (1987-08-01), Folsberg
patent: 4869786 (1989-09-01), Hanke
patent: 4919795 (1990-04-01), Fujii et al.
Fujii Satoru
Ito Mitsuhiro
Tamashige Takamiki
Bollinger David H.
Onodo Cement Co., Ltd
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