Solid material comminution or disintegration – Processes – Application of solids to material
Reexamination Certificate
1999-09-13
2001-04-10
Tolan, Ed (Department: 3725)
Solid material comminution or disintegration
Processes
Application of solids to material
C106S739000, C106S757000
Reexamination Certificate
active
06213415
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to the use of additives for the grinding of cement clinker, and more particularly to the use of at least one high molecular weight polymer in mills that employ rollers for grinding the cement clinker and optional further pozzolanic materials.
BACKGROUND OF THE INVENTION
U.S. Pat. No. 5,720,796 of Cheung et al. disclosed grinding aids for treating blast furnace slag feed of roll presses using 0.002 to 0.2 weight percent of polyacrylic acid or its alkali metal salt in combination with up to about 4 weight percent water. Such roll presses are comprised of opposed rollers through which granulated blast furnace slag is fed and ground into finer particles.
The present invention, on the other hand, concerns the grinding of cement clinker which may optionally be interground with other agrillaceous materials such as clay or pozzolanic materials such as natural pozzolan, flyash, limestone, blast furnace slag, and others. The present invention therefore contemplates a different grinding material with different hardness and morphology than the granulated blast furnace slag. In this case, cement clinker is provided in the form of spheroids having an average diameter of 1-3 cm.
The present invention may also be applied to the use of roller mills which employ rollers in an arrangement different from roll presses. Roller mills have sets of grinding rollers that rotate above a grinding table which travels in a circular path, and a classifier that is mounted above the rollers and the grinding table.
Roller mills are designed to pulverize and classify solid materials such as clays, clinker, gypsum, natural pozzolan, limestone, and blast furnace slag. A typical roller mill thus has a set of rollers, a roller table typically ranging from 30 inches to 200 inches in diameter, and a classifier component in one circular housing unit or enclosure. An example is shown in FIG. 1 of U.S. Pat. No. 3,951,347 which is incorporated herein by reference. Roller mills are used for raw materials grinding and finished material grinding in cement manufacturing plants. In the grinding of both raw and finished materials, the materials are conveyed or fed to the center of the roller table and become distributed on the table surface to form a bed or layer of material. Centrifugal force of the unit moves the materials from the center of the table to the outer table rim. As the bed of material passes between the rollers and table, the material becomes progressively pulverized. When the ground materials reach the rim of the grinding table, the lighter and smaller particles are conveyed upwards by an air stream into a cyclone as products, while the heavier and coarser particles drop through the slots and are eventually re-circulated back to the center of the table for re-grinding.
Frequently, the action of the large sets of rollers on the table generates vibrations, and this is said to occur because the bed of material located between the rollers and table do not form a layer having uniform thickness or because a gust of air is generated at the back of the rollers after compaction of the bed materials by the grinding rollers. Many manufacturers have tried to improve the grinding efficiency or bed stability by increasing the frictional forces between the table, material bed, and rollers such as through changes in roller pattern and table design.
One of the objectives of the present invention is to improve the stability and uniformity of the material bed by chemical means, thereby improving the efficiency by which the cement clinker is ground by the rollers.
It is another objective of the present invention to improve the grinding performance, in general, of roller-type mills which employ the stress forces of rollers to comminute cement clinker, alone or in combination with other agrillaceous materials such as clay or pozzolanic materials such as natural pozzolan, flyash, limestone, blast furnace slag or mixture thereof.
SUMMARY OF THE INVENTION
The present invention pertains to the use of a binding-densifying agent to improve the grinding operations in which cement clinker, either alone or in combination with an agrillaceous materials such as clay or pozzolanic material comprising natural pozzolan, limestone, blast furnace slag, or mixture thereof, is ground into cement particles using rollers. It is believed that grinding efficiency of roller-actuated comminution of particulate material is provided; and, where the grinding operation involves roller mills especially, the uniformity and stability of the materials bed on the grinding table is significantly improved to the point at which vibrations of the roller mills are reduced.
An exemplary process of the invention comprises introducing a cement clinker into grinding contact with rollers operative to grind the clinker into cement particles; and introducing to said clinker or said rollers, in an amount of 0.001-0.5 percent based on the dry weight of the cement clinker being introduced to said rollers, a binding-densifying agent comprising at least one polymer having an average molecular weight of 50,000-500,000
The feed stream of clinker into milling operations usually involves particles having an average diameter of 1-3 cm. The clinker is ground into smaller particles having a mean particle size of about 100-1000 microns. The binding-densifying agents contemplated in the invention are needed for attaching to the cement particles throughout various size ranges, such that, when compacted (i.e., densified because of greater mass/volume ratio), both the uniformity of the material bed of clinker/particles and grinding efficiency are improved. The binding-densifying agent polymer may be introduced into the pozzolanic material before it is deposited onto the rollers or grinding surface, or onto the layer of material after it has been deposited between opposed rollers (such as in a roll press) or between rollers and grinding table surface (such as in a roller mill). The polymer may even be introduced into the air stream (roller mill) swirled about or above the roller and grinding table surface.
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POLYCOM® ensures trouble-free and highly economical operation, 2 pages.
Baker William L.
Leon Craig K.
Tolan Ed
W.R. Grace & Co.-Conn.
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