This invention relates to rolls, and more specifically to an energy-efficient grinding roll of the type that is intended to be used in pulverizers for purposes of effecting therewith the pulverization within the pulverizer of material such as, for example, coal.
An essential component of any steam generation system of the type, which utilizes coal as a fuel, is the apparatus in which the coal is pulverized in order to render it suitable for such usage. Although the prior art is replete with examples of various types of apparatus that have been employed for purposes of accomplishing coal pulverization, one form of coal pulverizer, which in particular has frequently been used for this purpose, is that commonly referred to as a bowl mill. The latter obtains its name principally from the fact that the pulverization, i.e., grinding, of the coal that takes place therewithin occurs on a grinding surface, which insofar as configuration is concerned resembles that of a bowl.
For an exemplary showing of a prior art form of bowl mill, reference may be had to U.S. Pat. No. 4,706,900 entitled "Retrofitable Coiled Spring System," which issued on Nov. 17, 1987 and which is assigned to the same assignee as the present invention. U.S. Pat. No. 4,706,900 contains a teaching of both the nature of the construction and the mode of operation of a bowl mill that is suitable for use for purposes of effecting the pulverization of the coal that is used to fuel a coal-fired steam generator. As set forth in this patent, the essential components of such a bowl mill are a body portion, i.e., housing within which a grinding table is mounted for rotation, a plurality of grinding rolls that are supported in equally spaced relation one to another, the plurality of grinding rolls are suitably arranged in such a manner so as to coact with the grinding table such that coal which is disposed on the surface of the grinding table is capable of being ground, i.e., pulverized, by the rolls, coal supply means for feeding to the surface of the grinding table the coal which is to be pulverized in the bowl mill, and air supply means for providing to the interior of the body portion the air that is required in the operation of the bowl mill.
In order to satisfy the demands for pulverized coal of a coalfired steam generation system that embodies a conventional form of construction, there commonly exists a need to employ a plurality of bowl mills of the type which are shown in the aforereferenced patent. In this regard, note is further made here of the fact that in terms of capacity each of these bowl mills may have a capacity of up to one hundred tons of pulverized coal. In addition to possessing the capability of operating at its maximum capacity, each of these bowl mills must also be capable of operating at less than full capacity, i.e., at some percentage thereof, e.g., 25%, 50%, 75%, etc. Finally, these bowl mills must also be capable of use with a variety of types of coal that have dissimilar grinding characteristics.
With further reference to the aforementioned patent, there is depicted therein grinding rolls that embody one type of construction. Over the years, however, grinding rolls embodying many other different types of construction, in addition to that depicted in the aforementioned patent, have been proposed for use in the bowl mills. In this regard, by way of exemplification and not limitation, one such other type of construction of grinding rolls of the kind that are intended to be utilized in bowl mills forms the subject matter of U.S. Pat. No. 3,409,236 entitled "Segmented Grinding Roll Assembly," which issued on Nov. 5, 1968 and which was assigned to the same assignee as the present invention. In accordance with the teachings of U.S. Pat. No. 3,409,936, there is provided a grinding roll that is made up of a number of pieces or segments, which segments are secured to an inner cylindrical member by means of nuts and bolts. The heads of the bolts are cast integrally with the segments. Malleable metal washers are positioned between each segment and the inner cylindrical member to ensure a tight fit between the segments and member.
By way of exemplification and not limitation, another such type of construction of grinding rolls of the kind that are intended to be utilized in bowl mills forms the subject matter of U.S. Pat. No. 4,181,264 entitled "Centrifugally Or Static Cast Grinding Rolls," which issued on Jan. 1, 1980 and which is assigned to the same assignee as the present invention. In accordance with the teachings of U.S. Pat. No. 4,181,264, there is provided a grinding roll wherein the grinding surface of the grinding roll is made up of a removable roller sleeve, which is securely held on the journal bearing housing by means of wedge lock rings located at each end of the roller sleeve. These wedge lock rings, along with the roller sleeve, can be easily assembled, and provide positive locking of the removable roller sleeve onto the journal bearing housing, even if there are slight irregularities on the tapered surfaces of the roller sleeve.
By way of exemplification and not limitation, yet another such type of construction of grinding rolls of the kind that are intended to be utilized in bowl mills, and more specifically, the method of manufacture thereof forms the subject matter of U.S. Pat. No. 4,389,767 entitled "Method Of Manufacturing Pulverizer Rolls," which issued on Jun. 28, 1983 and which is assigned to the same assignee as the present invention. In accordance with the teachings of U.S. Pat. No. 4,389,767, there is provided a method that is particularly suited for manufacturing a grinding roll of the type, which is designed to be embodied in a bowl mill so as to be operative therein for purposes of effecting the pulverization of a material such as coal through the coaction of the grinding roll with another surface with which the bowl mill is provided for this purpose. The subject method includes the steps of forming from a material that is characterized by its ease of machinability a body having the general configuration of a grinding roll, providing through the center of the body a suitably dimensioned through passage capable of having a support member positioned therewithin in mounted relation thereto, shaping the outer surface of the body in accordance with the predicted wear characteristics that the grinding roll is expected to experience based on the nature of the use to which the grinding roll is intended to be put such that the contour thereof replicates that of a worn grinding roll, and applying a substantially uniform layer of a material characterized by its wear-resistant qualities to the outer surface of the body.
By way of exemplification and not limitation, yet still another such type of construction of grinding rolls of the kind that are intended to be used in bowl mills forms the subject matter of U.S. Pat. No. 4,604,781 entitled "Highly Abrasive Resistant Material And Grinding Roll Surfaced Therewith," which issued on Aug. 12, 1986 and which is assigned to the same assignee as the present invention. In accordance with the teachings of U.S. Pat. No. 4,604,781, there is provided a grinding roll that has its external surface fabricated from an alloy, which is characterized by its highly abrasive resistant qualities. This alloy from which the external surface of the grinding roll is fabricated is capable of being cast or applied to the grinding roll in the form of a weld overlay and comprises, by weight percentages, 4.0-6.0% Carbon; 3.0-14.0% Manganese; 1.0-2.5% Silicon; 15.0-30.0% Chromium; and 4.0-6.0% Molybdenum; with 0.5%-2.0% Boron being added thereto, the balance being iron and incidental impurities.
By way of exemplification and not limitation, yet further still another such type of construction of grindingrolls of the kind that are intended to be utilized in bowl mills forms the subject matter of U.S. Pat. Nos. 4,610,073 and 4,610,401. That is, U.S. Pat. No. 4,610,073 is directed to the method of manufacture of the grinding roll and to this end is entitled "Trimetal Pulverizer Roll And A Method Of Manufacture Thereof." U.S. Pat. No. 4,610,073 issued on Sep. 9, 1986 and is assigned to the same assignee as the present invention. Moreover, U.S. Pat. No. 4,610,401 is directed to the grinding roll per se and to this end is entitled "Trimetal Pulverizer Roll." U.S. Pat. No. 4,610,401 also issued on Sep. 9, 1986 and also is assigned to the same assignee as the present invention. In accordance with the teachings of U.S. Pat. No. 4,610,073, there is provided a method of manufacturing a grinding roll, which has a trimetal form of construction and which is of the type suitable for use in a bowl mill for purposes of effecting the pulverization therewith of a material such as coal. The subject method includes the steps of forming from a material that is characterized by its ease of machinability a body having the general configuration of a roll, providing through the center of the body a suitably dimensioned through passage capable of having a shaft-like support member positioned therewithin in mounted relation thereto, affixing in supported relation to the body a first substantially uniform layer of material having medium wear-resistant characteristics, and affixing in supported relation to the first layer of material a second substantially nonuniform layer of material having highly abrasive resistant characteristics. On the other hand, in accordance with the teachings of U.S. Pat. No. 4,610,401 there is provided a grinding roll of the type that is particularly suited for embodiment in a bowl mill wherein the grinding roll coacts with another surface within the bowl mill to effect the pulverization therewithin of a material such as coal. The subject grinding roll embodies a trimetal form of construction. More specifically, the core material, i.e., the first or inner layer, of the trimetal grinding roll consists of a relatively soft material that is noted for its good machinability. The next, i.e., second or intermediate, layer of the trimetal grinding roll comprises a material that has medium wear-resistant qualities. The last, i.e., third or outer, layer of the trimetal grinding roll comprises a material having highly abrasive resistant qualities.
Thus, although grinding rolls constructed in accordance with the teachings of the seven issued U.S. patents to which reference has been made hereinbefore have been demonstrated to be operative for the purpose for which they have been designed, there has nevertheless been evidenced a need for such grinding rolls to be improved. To this end, recent industry trends with regard to the coal being demanded thereby is having the effect of necessitating that coal pulverizers and in particular those coal pulverizers commonly referred to as bowl mills possess the capability of being able to pulverize coal to a significantly finer degree than that which has been the conventional practice heretofore. Namely, in accordance with this trend, bowl mills more and more frequently are being required to possess the capability of being able to pulverize coal therewithin to newly established minimum fineness levels that are well below the fineness levels heretofore sought. The newly established minimum fineness levels to which reference is made here are the following: approximately 0% on a 50-mesh sieve, 1.5% on a 100-mesh sieve and more than 85% passing through a 200-mesh sieve. It is to be noted in this regard that to those who are skilled in this industry the size of a 50-mesh sieve, a 100-mesh sieve and a 200-mesh sieve are known to be such as to permit in accordance with established practice the passage therethrough of particles having a size of approximately 300 microns, 150 microns and 74 microns, respectively.
In order to be able to satisfy this demand for pulverized coals that are significantly finer than those that have been demanded before, it has been found that the bowl mills, which heretofore have commonly been employed for purposes of effecting therewith the pulverization of the coal, must be modified in order to possess the capability of producing such finer coals. To this end, in the case of existing bowl mills commonly such modification involves the retrofitting of the existing bowl mill with what those in the industry refer to as a rotary classifier. Similarly, new bowl mills frequently now incorporate therein a rotary classifier as original equipment. However, providing such significantly finer pulverized coal has not been able to be accomplished heretodate without adversely impacting the performance of the bowl mill, which is utilized to accomplish the pulverization of the coal to such significantly finer levels. Namely, it has been found that in order to achieve the fineness levels of coal that are being demanded, the grinding energy required to be expended by the bowl mill to achieve such fineness levels of coal is considerably more than the grinding, energy that must be expended by the bowl mill for purposes of accomplishing the pulverization of coals to lesser fineness levels.
In addition to the fact that significantly more energy is required to be expended by the bowl mill in order to accomplish the pulverization of the coal to such minimum fineness levels, another phenomena, referred to as "rumble" for lack of a better description of this phenomena, has proven to be something that can also serve to disadvantageously characterize the operation of a bowl mill when the bowl mill is being utilized to pulverize coal to the minimum fineness that the pulverized coal is now being required to possess in order to satisfy the demands of industry. "Rumble" is essentially a phenomena wherein the bowl mill produces a rumbling noise accompanied by significant vibrating of the bowl mill, which in turn conceivably can result in damage being suffered by the bowl mill as well as by surrounding equipment, etc., if the "rumble" is not eliminated. To date, "rumble" appears to be a phenomena that is encountered principally in bowl mills that are being employed to pulverize coal to fineness levels significantly below the fineness levels that had heretofore been sufficient to satisfy the demands of industry.
To thus summarize, a need has been evidenced in the prior art for an energy-efficient grinding roll that would be particularly suited for use in pulverizers, and in particular bowl mills, for purposes of effecting the pulverization therein of material such as, for example, coal. Moreover, such an energy-efficient grinding roll could be being employed in bowl mills for purposes of effecting therewith the pulverization of coal to fineness levels significantly below the fineness levels that had heretofore been sufficient to satisfy the demands of industry. Furthermore, through the use of such an energy-efficient grinding roll energy savings would be attainable when such an energy-efficient grinding roll is being employed in bowl mills for purposes of effecting therewith the pulverization of coal to the fineness levels that had heretofore been sufficient to satisfy the demands of industry. Last but not least, such an energy-efficient grinding roll would be operative when employed for purposes of effecting the pulverization of coal therewith in bowl mills equipped with rotary classifiers to inhibit the initiation of "rumble" within such bowl mills when the bowl mills are being operated under normal conditions.
It is, therefore, an object of the present invention to provide a new and improved form of grinding roll of the type that is intended to be used in pulverizers, and in particular bowl mills, for purposes of effecting the pulverization therein of material such as, for example, coal.
It is another object of the present invention to provide such a grinding roll, which is characterized in that energy savings on the order of at least 15% are attainable through the use thereof in a bowl mill.
It is still another object of the present invention to provide such an energy-efficient grinding roll, which is characterized in that energy savings are attainable therewith when such an energy-efficient grinding roll is being employed in bowl mills for purposes of effecting therewith the pulverization of coal to fineness levels below those that had heretofore been sufficient to satisfy the demands of industry.
A further object of the present invention is to provide such an energy-efficient grinding roll, which is characterized in that energy savings are attainable therewith when such an energy-efficient grinding roll is being employed in bowl mills for purposes of effecting therewith the pulverization of coal to the fineness levels that had heretofore been sufficient to satisfy the demands of industry.
A still further object of the present invention is to provide such an energy-efficient grinding roll, which is characterized in that when such an energy-efficient grinding roll is employed for purposes of effecting the pulverization of coal therewith in bowl mills equipped with rotary classifiers such an energy-efficient grinding roll is operative to inhibit the initiation of "rumble" within such bowl mills when the bowl mills are being operated under normal conditions.
A still another object of the present invention is to provide such an energy-efficient grinding roll, which is suitable for employment in a bowl mill that embodies a rotary classifier.
Yet an object of the present invention is to provide such an energy-efficient grinding roll, which is suitable for employment in a bowl mill that does not embody a rotary classifier.
Yet a further object of the present invention is to provide such an energy-efficient grinding roll, which is suitable for installation in new bowl mills.
Yet another object of the present invention is to provide such an energy-efficient grinding roll, which is capable of being retrofitted into existing bowl mills.
Yet still another object of the present invention is to provide such an energy-efficient grinding roll, which is relatively inexpensive to provide, is easy to employ and is characterized by the energy savings that are attainable therewith as compared to the energy savings, if any, that have been possible to be realized from the grinding rolls which have heretofore been available for use for similar purposes.