BACKGROUND OF THE INVENTION

The invention relates to a closed-circuit grinding plant for grinding coarse material into a fine material, in particular for generating cement raw meal and/or cement from cement clinker, the plant having at least one roller press for pulverizing the coarse material, at least one sifter for separating the fine material generated during the pulverization from the remaining coarse material, and at least one fine material settling device for settling the fine material from the sifting air of the sifter.

For the grinding of coarse material into a fine material, it is known to design closed-circuit grinding plants as vertical roll mills or as roller presses, the circuit of the material to be ground being generated by a bucket conveyor or other elevators. In the closed-circuit grinding plants, the fine material is separated from the coarse material by air sifters.

However, these plants are usually not scalable and have to be completely shut down for maintenance.

SUMMARY OF THE INVENTION

The object of the invention is to provide a closed-circuit grinding mechanism which is scalable and can be maintained during operation.

â€œDeletedâ€ .

The closed-circuit grinding plant according to the invention is composed of more than one peripheral roller press which together form a roughly circularly symmetrical closed-circuit grinding system in the plane perpendicular to the vertical. In this case, individual roller presses can be deactivated during operation so as to allow the individual roller presses to be maintained. For this purpose, the feeding of material to be ground to the corresponding roller press is suspended and the closed-circuit grinding plant as a whole thus operates at reduced but not switched-off capacity.

The closed-circuit grinding plant according to the invention is easily scalable. The individual roller presses and their spares may be stocked as standardized individual parts.

In addition, the closed-circuit grinding plant according to the invention is suitable for replacing vertical roll mills, as their dimensions are comparable and, on account of a higher pressure in the roller nip compared to the pressure between the plate roller and the grindstone of a vertical roll mill, the capacity is greater than that of a vertical roll mill, as the number of revolutions of the material to be ground is reduced as a result of the higher nip pressure.

The grain size distribution of the ground fine material is also narrower as a result of the lower number of revolutions, leading to advantageous properties of the cement produced by the mill according to the invention.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will be described in greater detail with reference to the following figures, in which:

FIG. 1 shows a closed-circuit grinding plant according to the invention with four roller presses in a fourfold configuration,

FIG. 2 is an enlarged detailed view of the roller presses and riser pipe of FIG. 1,

FIG. 3 shows a closed-circuit grinding plant according to the invention with four roller presses in an eightfold configuration,

FIG. 4 is an enlarged detailed view of the roller presses and riser pipe of FIG. 3.

DETAILED DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a closed-circuit grinding plant according to the invention having four roller presses 1a, 1b, 1c and 1d arranged symmetrically around a central riser pipe 2 for pneumatically conveying the circulating material to be ground.

Coarse material to be ground is fed into a central rod basket sifter 3 arranged above the roller presses 1a, 1b, 1c and 1d centrally on the riser pipe 2. The coarse material issues from the side of the rod basket sifter 3 and is passed using feeders (not shown here) to the roller mills 1a, 1b, 1c and 1d. There, the coarse material is pulverized and falls into the cascade sifters 4a and 4b below the roller presses 1a, 1b, 1c and 1d via feeders (not shown here). In the cascade sifters 4a and 4b, the coarse material is separated from the fine material, the coarse material issuing downward out of the cascade sifters 4a and 4b and the coarse material provided for a further revolution being transported back upward to the rod basket sifter 3 using an elevator (not shown). The fine material is, on the other hand, transported pneumatically through the central riser pipe 2 also into the rod basket sifter 3 and, from there, into the four cyclones 5a, 5b, 5c and 5d. There, the fine material is separated from the sifter air, and the sifter air purged of fine material leaves the closed-circuit grinding plant from the cyclones 5a, 5b, 5c and 5d. The sifter air is discharged through the collector 6 almost without dust.

FIG. 2 is an enlarged detailed view of the roller presses 1a, 1b, 1c and 1d from FIG. 1.

FIG. 3 shows a closed-circuit grinding plant comparable to FIG. 1 but with eightfold symmetry.

FIG. 4 is an enlarged detailed view of the roller presses 100a, 100b, 100c, 100d, 100e, 100f, 100g and 100h from FIG. 3.

As is apparent from the foregoing specification, the invention is susceptible of being embodied with various alterations and modifications which may differ particularly from those that have been described in the preceding specification and description. It should be understood that we wish to embody within the scope of the patent warranted hereon all such modifications as reasonably and properly come within the scope of our contribution to the art.