Solid material comminution or disintegration – Processes – With application of fluid or lubricant material
Reexamination Certificate
1998-02-09
2001-02-27
Rosenbaum, Mark (Department: 3725)
Solid material comminution or disintegration
Processes
With application of fluid or lubricant material
C241S024100, C241S080000
Reexamination Certificate
active
06193176
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to a cement clinker grinding method using a vertical roller mill and a cement clinker grinding apparatus, by which cement clinkers and cement materials are ground and produced as cement products by use of the vertical roller mill.
FIG. 24
shows a prior art vertical roller mill which has been used for producing the cement products by grinding the cement clinkers, the cement materials and so on. In
FIG. 24
, a vertical roller mill
1
of so-called separator built-in type includes a housing
2
, a table
3
arranged in the housing
2
so as to rotate about a vertical axis and a motor
4
for rotating the table
3
. A plurality of rollers
5
are pressed on the table
3
. In the housing
2
, a separator
6
is arranged above the table
3
and the rollers
5
. Feed material to be ground, which has been supplied from a material chute
7
, is ground between the table
3
and the rollers
5
. Air is introduced into a clearance
8
defined between an outer periphery of the table
3
and an inner periphery of the housing
2
in order to blow up the ground material by a resultant air flow
9
. The ground material blown up is classified in the separator
6
, so that the fine powder as the products is conveyed by air flow through a pipe line
10
. As shown with an arrow
11
, the coarse powder is returned onto the table
3
for circulation and ground thereon again.
In the above-mentioned vertical roller mill
1
of
FIG. 24
, the pressure of the roller
5
per full sectional area of roller is established to be less than about 8 kg/cm
2
. Such an establishment of the roller pressure allows the resultant products to have a particle size suitable for the cement and makes a basic unit of power satisfactory.
Further more, in the prior art vertical roller mill
1
, a circulation ratio of the ground material (alias, a ratio of grinding occasion, that is, a ratio of a flowing amount of the coarse powder returned from the separator
6
onto the table
3
to a flowing amount of feed material charged into the vertical roller mill through the material chute
7
) is estimated more than 1000 per cent (%), so that the coarse powder is instantly returned onto the table
3
for grinding it again. Thus, as an example, in order to realize the grinding amount of 100 ton/hour, the ground material over 1000 ton/hour has to be conveyed with air flow.
One problem to be solved in the conventional vertical roller mill
1
of
FIG. 24
resides in narrow particle-size distribution of the products obtained through the pipe line
10
. Particularly, regarding the operation for grinding the cement clinkers, the particle size distribution of the products has a great influence on the quality of products. In the above-mentioned prior art, when the particle-size distribution varies due to the aged deterioration etc., it is difficult to adjust the particle-size to distribution properly.
Since the conventional vertical roller mill
1
of
FIG. 24
has a small production ratio of the fine powder, the resultant products have a great deal of intermediate particles in comparison with the product obtained by a tube mill. Thus, there exists such a tendency that (n) value of Rosin-Rammler diagram is large, thereby producing the products characterized by a narrow particle-size distribution. The cement products having a narrow particle-size distribution causes the quantity of water required for the standard softness, the concrete experiment etc. to be increased, so that the quality of cement products would be deteriorated.
The other problem of the vertical roller mill of
FIG. 24
resides in largeness of air-swept, that is, the power consumption of suction fan for air flow conveyance is too large. As mentioned above, in order to convey the ground material to the separator
6
inside the housing
2
and subsequently classify the material therein, the material ground between the table
3
and the rollers
5
has to be blown up by a great flow of air introduced from the underside of the table
3
through the clearance
8
. Therefore, the pressure loss within the vertical roller mill
1
is relatively large, and further the power consumption of the suction fan is also very large.
The other problem of the vertical roller mill
1
of
FIG. 24
resides in lowered temperature of the products. The vertical roller mill
1
is constructed in a manner that a large amount of cool air is introduced for air flow conveyance of the ground material. Therefore, because of the progressed cooling performance, the temperature of the ground material is lowered. It is noted that, together with the cement clinkers, gypsum is also contained in the material to be ground. By lowering the temperature, this gypsum becomes to be the cement products as it is dihydrate gypsum. Generally, it is desirable that the crystallization water of gypsum is transformed into either hemihydrate gypsum or anhydrate gypsum during the grinding process. As a result, a problem arises in that there exists a possibility of false cement setting due to the dihydrate gypsum. Therefore, in order to prevent the false cement setting, an installation for either introducing hot air from the outside or circulating exhaust gas from the suction fan would be required. In such a case, the installation cost would be increased with an increased capital investment.
SUMMARY OF THE INVENTION
Accordingly, it is therefore an object of the present invention to provide a cement clinker grinding method by use of a vertical roller mill and a cement clinker grinding apparatus including the vertical roller mill, both of which are capable of miniaturizing the size of an installation including the vertical roller mill; improving the quality of products by broadening the conventional particle-size distribution of the products, thereby realizing the particle-size distribution suitable for the cement products and reducing the power required for the suction fan and solving the problem of false cement setting.
The object of the present invention described above can be accomplished by a method of grinding cement clinkers by use of a cement clinker grinding apparatus; the method comprising the steps of:
preparing the cement clinker grinding apparatus comprising:
a vertical roller mill having a table for rotating about a vertical axis and a plurality of rollers arranged on the table at circumferential intervals in a rotating direction of the table, the vertical roller mill being constructed in a manner that feed material to be ground is supplied on a central area of the table, subsequently ground the feed material between the table and the rollers for producing ground material and thereafter, substantially all of the ground material is taken out from an underside of the table;
a separator for classifying the ground material ground by the vertical roller mill; and
mechanical conveyer means for conveying at least a part of the ground material taken out of the vertical roller mill to the separator mechanically;
grinding the feed material by pressing force of each of the rollers onto the table, the pressing force being selected so that a roller pressure per full sectional area of the roller ranges from 10 to 15 kg/cm
2
.
According to the present invention, substantially all of the ground material, which has been ground by the vertical roller mill, is taken out from the underside of the table and subsequently conveyed by the mechanical conveyor means which does not utilize pneumatic force, such as a bucket elevator, a screw conveyor, a chain conveyor etc. Then, at least a part of the ground material is fed to the separator, so that the coarse powder obtained in the separator is returned to the vertical roller mill for circulation. The separator is disposed outside of the vertical roller mill. The separator may be an air-flow type of separator utilizing pneumatic force. Alternatively, either a separator having a sieve or the other may be adopted as the separator.
Therefore, according to the invention, since the pressure loss at the mill is remarkably reduced as compare
Ando Fuminori
Mitsuda Yoshihiro
Murata Mitsuaki
Sawamura Seisuke
Sutoh Kanzaburo
Kawasaki Jukogyo Kabushiki Kaisha
Oliff & Berridg,e PLC
Rosenbaum Mark
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