The present invention relates to a separator for sorting particulate material into coarse and fine fractions, e.g. raw materials of cement or cement clinker or similar mineral raw materials which have been ground under high pressure in a roller press, resulting in that the ground material contains agglomerates which have to be desagglomerated before the material can be further treated.

Separators for sorting out a fine fraction from a coarse fraction of ground, particulate material are disclosed e.g. in the form of air separators in i.a. AU patent No. 220,069, DE patent No. 1,913,946, EP patent specification No. 0,023,320 and EP patent specification No. 0,210,729 and in Duda: Cement Data Book 1, chapter 15 (3rd edition, Bauverlag GmbH, Wiesbaden and Berlin, 1985). When using such air separators in their present form of single separators in connection with roller presses, the material charge has usually been subjected to a separate desagglomeration process, e.g. in a hammer mill, prior to the separation process in order to disintegrate the agglomerates, which entails an increase in the number of individual machines in the grinding plant and wear and tear of the hammer mill. The inevitable dust formation in the hammer mill causes dust-laden material to be conveyed to the separator.

As a continuously increasing part of the grinding tends to take place in the roller press this furthermore results in that the separator has to treat a continuously increasing amount of material due to an increase in the closed-circuit rate. As a result the material concurrently becomes coarser which again results in increased wear and tear and an even higher power consumption in the separator.

When subsequently using a tube mill in such prior art single separator plants to comminute the separated roller-pressed material charge into fine particles, the material supplied to the tube mill has up to now either been characterized in containing large single particles, which require large grinding bodies in the tube mill, or the tube mill has been fed with semi-ground material of a relatively high fineness, resulting in the dry material tending to clog in the tube mill .

It is therefore the object of the present invention to provide a separator which can be used together with a roller press and optionally together with a tube mill and in which the above mentioned drawbacks are avoided.

The object is obtained by means of a separator of the type mentioned in the introductory part of claim 1 and which is characterized by the subject matter of the characterizing part of the claim.

Further features of the separator will appear from the contents of claims 2-5.

Such a separator allows for an increase in the feed load from the roller press to the coarse separator higher than that for a separator of the single separator type as the coarse material charge from the roller press is supplied directly to the separator without preceding desagglomeration in a separate desagglomerator. Furthermore, a relatively high separation degree (low "cut size") is obtained with the coarse separator, which relieves the fine separator so that a low specific separator effect for the separator as a whole is obtained.

The coarse fraction of the coarse material which is separated in the coarse separator is returned to the roller press, thereby increasing the possibilities of utilizing said press more efficiently while the coarse fraction of the fine material being separated in the fine separator is fed to the tube mill being a closed-circuit mill of the single-chamber type using small grinding bodies, thereby resulting in an improved tube mill efficiency due to the fact that neither great single particles nor ultra fine material, but merely a medium fraction of material is supplied to the tube mill.

The invention will now be explained in further detail in the form of an example and with reference to the drawing in which

Fig. 1 shows a vertical section through a double separator according to the invention and

Fig. 2 shows more detailed a part of the lowermost separator.

The double separator consists of a coarse separator 2, on top of which a fine separator 1 is mounted, the circumference of the top of the housing 13 of the separator 2 corresponding to the circumference of the bottom of the housing 9 of the separator 1 so that a suspension of material-gas is allowed to pass directly from the separator 2 into the separator 1. A suspension outlet duct 3 in which inside fittings 4 may be inserted to reduce the pressure loss is provided at the top of said separator 1. A vertical driving shaft 5 connected to driving means (not shown) causes the rotor 7 of the separator 1 to rotate. Outside the rotor 7 and along the circumference of said rotor the separator 1 is provided with louvre blades 6 which are adjustable so that the position of the louvre blades, the velocity of the rotor and the amount of supplied air can be adjusted to the desired degree of separation of material from the gas stream. Apart from the amount of material supplied to the separator 1 via the conveying gas from the separator 2, the separator 1 may be charged with material via the inlet duct 11 which is connected to a tube mill (not shown), to which mill the separator 1 is in closed circuit. Sorted coarse material which is separated ro the suspension after treatment of the suspension in the separator 1 is directed to the tube mill via the hopper 8 and the outlet duct 10, or optionally to the roller press for renewed comminution.

The separator 2 has an inlet duct 15 which is connected to a roller press (not shown) in which the material charge is comminuted under high pressure so as to form i.a. agglomerates. The treated material is fed directly from the roller press into the rotor of the separator 2 via the inlet duct 15. Said rotor is a horizontal, centrifugal impact pulverizer which throws the agglomerate- containing material towards the stationary vertical rotor wall 16' by means of rotating arms 16 (vide Fig. 2), thereby causing at least the material agglomerates to be crushed by impact against the wall 16'. After the impact against the wall 16' the treated material falls downwards outside the rotor, which apart from the impact pulverizer or desagglomerator also consists of the drive shaft 22. Moreover the rotor may have an outwardly extending cone 19. The coarse material separator may furthermore be provided with one or more sets of adjustable louvre blades 17. During the passage of the

material down between the rotor and the louvre blades the finer part of the fraction is caught by the conveying gas which is fed to the coarse separator 2 via the tangential inlet 18 and conveyed together with the gas up through the spaces between the arms 16 of desagglomerator and further through the housing parts 14 and 13 up into the fine separator 1 via a dispersing part 12, whereas the coarse part of the fraction from the coarse separator 2 is conveyed into the outlet duct 21 via the hopper 20 and from the outlet duct back to the roller press for renewed comminution.

The desagglomerator rotor may be a centrifugal pulverizer of a known type and in which pulverization may also be effected by impact of discharged material against an impact cushion 24 formed by a material charge deposited on the inside of the rotor wall 16' (vide Fig. 2).

In a particular embodiment of the invention the cone 19 in the coarse separator 2 has a plurality of vanes 23 to increase the separation effect. Correspondingly the desagglomerator rotor in the spaces between the arms 16 may have vanes (not shown) to increase the separation effect.

The degree of separation ("cut size") in the coarse separator is adjusted in the manner similar to the one indicated above for the fine separator by regulating the amount of supplied air and gas and by adjusting the louvre blades and the rotor velocity. Additionally regulation may further be effected through the plurality of vanes on the cone 19 and between the rotor arms 16.