Circulating air classifier or separator

Circulating air classifier having a separator chamber containing an impeller rotatable about a vertical axis, and a funnel-shaped pre-separator disposed underneath and in open communication with the separator chamber. A blower forces air through a conduit. Material to be classified is fed into the air through an inlet in the conduit. The feed material and air enter the upper part of the pre-separator tangentially causing pre-separation, i.e. some coarse matter to separate. The air with the remaining feed material passes upwardly into the separator chamber wherein aided by the impeller further separation of coarse matter takes place. The air with the suspended fine material passes out of the separator chamber into cyclones wherein the fine material is separated from the air. The thus cleansed air is recirculated to the suction side of the blower.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
This invention relates to air classifiers for separating coarse and fine 
fractions of solid material and more particularly refers to a new and 
improved circulating air classifier with vertical axis in which the air 
blower is located outside the classifier separator and air containing fine 
material is transferred from the classifier separator to separating 
cyclones and the cleansed air recirculated to the blower. 
2. Description of the Prior Art 
A vertical axis air classifier is one in which the rotating components are 
carried on a vertical shaft. In a circulating air classifier with vertical 
axis, the sifting or classifier air is moved by a blower outside the 
separator housing. The material to be separated is fed to a rotating 
spreading disc within the separator chamber, which throws the material to 
be separated into the separator chamber and thereby spreads it uniformly 
in veil-fashion over the entire separator area, so that the air stream 
helically rising in the separator chamber can seize the dust to be 
separated as completely as possible and remove it from the separator 
chamber. Under the influence of centrifugal and gravity forces, the coarse 
matter leaves the separator chamber in a downward direction via a 
collecting funnel. 
In this classifier, all the material to be separated is conducted into the 
separator chamber. This is a disadvantage particularly if the material to 
be separated has percentagewise fewer fine components than coarser 
material. As a result, the separator chamber is unnecessarily loaded, 
whereby the efficiency of the separation process is adversely affected. 
Thus, it is most difficult if not impossible to separate the coarse matter 
sharply from finer material in the feed material undergoing 
classification. This factor of sharp separation of the coarse matter, 
however, is important for the production of flour-free grit, if the latter 
is to be returned to a mill for further grinding. The coarser grains also 
cause heavy wear at the spreading disc and at the blades of the 
centrifugal system arranged above the spreading disc. 
SUMMARY OF THE INVENTION 
An object of the present invention is to provide a circulating air 
classifier with vertical axis which will efficiently effect sharp 
separation of coarse matter from fine material in the feed material. 
With the foregoing and other objects in view, there is provided in 
accordance with the invention a circulating air classifier with vertical 
axis having 
(a) a separator chamber in which coarse matter is separated from fine 
material, 
(b) an impeller rotatable about the vertical axis disposed in the separator 
chamber to aid in separating the coarse matter from the fine material 
suspended in air rising up through the separator chamber, 
(c) an opening in the bottom of the separator chamber through which the 
coarse matter discharges, 
(d) at least another opening in the separator chamber above the bottom 
through which the fine material suspended in air is discharged, 
(e) at least one cyclone for receiving said fine material suspended in air 
and separating the fine material from the air, 
(f) connecting means for conducting the fine material suspended in air from 
the opening in the separator chamber to the cyclone, 
(g) an air blower with an air suction inlet and a pressure discharge 
outlet, 
(h) an air return line connecting the cyclone to the suction inlet for 
recirculating air separated in the cyclone, 
(i) a funnel-shaped pre-separator chamber disposed underneath and in open 
communication with the separator chamber, 
(j) a compressed air-line with one end connected to the pressure discharge 
outlet of the air blower and the other end opening into the upper part of 
the funnel-shaped pre-separator with air from the air-line flowing 
tangentially into the pre-separator, 
(k) inlet means in the compressed air-line upstream from the funnel-shaped 
pre-separator for the introduction of feed matter, which together with air 
flowing from the air blower enters the pre-separator tangentially causing 
coarse matter to be separated from the feed matter, and 
(l) outlet means in the lower part of the pre-separator for the discharge 
of the coarse matter. 
Other features which are considered as characteristic for the invention are 
set forth in the appended claims. 
Although the invention is illustrated and described herein as embodied in a 
circulating air classifier or separator, it is nevertheless not intended 
to be limited to the details shown, since various modifications may be 
made therein without departing from the spirit of the invention and within 
the scope and range of equivalents of the claims.

DETAILED DESCRIPTION OF THE INVENTION 
In accordance with the invention, it is important that the compressed-air 
line coming from the blower leads tangentially into the upper part of the 
collecting funnel or pre-separation chamber and that the material to be 
separated is fed into this pressure line, optionally via a distribution 
device. This relieves the separator chamber above the pre-separating 
chamber of handling all the feed material, and since the quantity of 
material passing through the separator chamber is substantially reduced, 
the separating effect is substantially increased thereby. It is also 
possible to separate fractions (fine, medium and coarse product) with this 
air separator. 
In a further embodiment of the invention, a post-separator chamber for 
coarser material discharged on the collecting funnel may be arranged 
underneath the collecting funnel. This post-separator is supplied with 
sifting or classifier air by way of a branch line of the blower pressure 
line thereby stripping fine material from the coarser material discharged 
on the collecting funnel and making for sharp separation. The coarse 
matter can also be collected from the separator chamber in a separate 
funnel within the collecting funnel and the coarse matter collected in the 
separate funnel and removed separately. 
In the drawings, the invention is depicted in two embodiment examples. 
The separator housing 1 in FIGS. 1 and 2 encloses with its upper part the 
separator chamber 2 and forms in the lower part the pre-separator chamber 
3, which is advantageously designed as a cyclone. In the separator chamber 
2, a centrifugal system 6, driven by the motor 5 via a transmission 4, is 
provided. The term "centrifugal-system" is commonly used in the German 
Sifter (Classifier) Industry, to connote an impeller wheel or fan wheel. 
The purpose of the centrifugal-system which will be designated in the 
claims as "impeller" it to increase the whirling motion of the rising 
sifter air, in order to increase or maintain the centrifugal forces of the 
heavier particles suspended in the air, so that these particles can be 
thrown to the outside and slide down along the outer wall of the separator 
chamber. The input or feed material is fed to the pre-separator chamber 3 
via the separator input 7 and a distributor 8, which is arranged in the 
form of staggered baffles in the compressed-air line 9 of the blower 10. 
The compressed air line 9 opens tangentially into the funnel-shaped 
pre-separator chamber 3, so that the latter acts like a cyclone. The 
coarse particles of the input material are immediately separated-out in 
the pre-separator chamber 3 by the centrifugal and gravity forces. 
The fine material (dust) which also contains some coarse material but is 
appreciably smaller in quantity than the input material, is fed to the 
separator chamber 2 by the air stream generated by the blower 10. In this 
chamber 2, the separation proper takes place by means of the 
variable-speed centrifugal system 6 which aids in further separating the 
coarse matter from the fine material by throwing the heavier particles to 
the outside. Separated coarse matter drops down through the open bottom of 
separator chamber 2. The sifted fine material suspended in air is fed from 
separator chamber 2 to the separator cyclones 12 via the connecting lines 
11. The fine material separated there leaves the cyclones 12 at the bottom 
at 13 via a conventional swinging vane not shown in the drawing. The 
sifting air is returned from cyclones 12 to the blower 10 via the 
connecting line 14. 
A post-separator chamber 15 is arranged in the lower part of the 
pre-separator chamber 3 to receive the coarse matter from chamber 3. The 
air fed-in into chamber 15 flows through the air line 16 and the rate of 
flow can be controlled with the damper 17. The guiding vanes 18 are 
provided for uniformly distributing the air entering chamber 15 and as the 
air passes in contact with the coarse matter therein stripping of the fine 
material is effected. The coarse matter leaves the separator via the 
outlet 19. Fresh air or also hot gases can be fed to the separator through 
the stubs 20 and 21. The exhaust air is fed to a filter, not shown, via 
the outlet 22 for removal of any solids in the air before discharge into 
the atmosphere. 
In the embodiment of the separator according to FIGS. 3 and 4, a further 
separator chamber 23 with guide vanes 24 which can be set from the outside 
to tangentially direct the sifting air and solids into chamber 23, is 
provided in the pre-separator chamber 3. Thereby, further preliminary 
sifting takes place in chamber 23 with some separation of the coarse 
matter. This coarse matter as well as the coarser material which is 
separated-out by post-separation in the separator chamber 2 leaves the 
separator via the collecting funnel 25 and the line 26.