LESNIAK THOMAS W (US)
MEUSEL JERRY (US)
LESNIAK THOMAS W (US)
| US6491751B1 | 2002-12-10 | |||
| US6264738B1 | 2001-07-24 | |||
| US4504319A | 1985-03-12 | |||
| US6709510B1 | 2004-03-23 | |||
| US5575827A | 1996-11-19 |
WHAT IS CLAIMED IS:
1. A process for producing cement clinker using a rotary cement kiln equipped with a preheater system having a feed end and an outlet end, wherein the outlet end of the preheater system is communicably connected to the rotary cement kiln; the process comprising introducing cement raw materials into the preheater system; wherein the cement raw materials include slag having a particle size in a range from about 1 mm to about 5 cm, and non-slag cement raw materials; and wherein the slag is selected from at least one member of the group consisting of steel slag, air cooled blast furnace slag, copper slag and zinc slag.
2. The process according to claim 1, wherein the non-slag cement raw materials have an average particle size that is less than about 100 microns.
3. The process according to claim 2, wherein the cement raw materials are introduced into the preheater system through the feed end of the preheater.
4. The process according to claim 3, wherein the cement raw materials are introduced into the preheater system using a mechanical conveying device.
5. The process according to claim 4, wherein the mechanical conveying device is a belt conveyer, a screw conveyer or a bucket elevator.
6. The process according to claim 2, wherein the slag is introduced into the preheater system using a mechanical conveying device and the finely ground non-slag cement raw materials are introduced into the preheater system using a pneumatic conveying device.
7. The process according to claim 6, wherein the mechanical conveying device is a belt conveyer, a screw conveyer or a bucket elevator.
8. The process according to claim 6, wherein the slag is introduced into the preheater system at an entry point between the feed end of the preheater and the outlet end of the preheater.
9. The process according to claim 1, wherein the preheater system comprises a preheater equipped with a precalciner.
10. The process according to claim 9, wherein the cement raw materials are introduced into the preheater system through the feed end of the preheater.
11. The process according to claim 10, wherein the cement raw materials are introduced into the preheater system using a mechanical conveying device.
12. The process according to claim 11 , wherein the mechanical conveying device is a belt conveyer, a screw conveyer or a bucket elevator.
13. The process according to claim 9, wherein the slag is introduced into the preheater system using a mechanical conveying device and the finely ground non-slag cement raw materials are introduced into the preheater system using a pneumatic conveying device.
14. The process according to claim 13, wherein the mechanical conveying device is a belt conveyer, a screw conveyer or a bucket elevator.
15. The process according to claim 13, wherein the finely ground non-slag cement raw materials are introduced through the feed end of the preheater and the slag is introduced into the precalciner.
16. The process according to claim 15, wherein the precalciner comprises a fuel port through which fuel is introduced into the precalciner, and the slag is introduced into the precalciner with the fuel through the fuel port.
17. The process according to claim 15, wherein the slag is introduced into the precalciner through a port other than a fuel port.
18. An apparatus for producing cement clinker comprising: a rotary cement kiln equipped with a preheater system having a feed end and an outlet end, wherein the outlet end of the preheater system is communicably connected to the rotary cement kiln; and a mechanical conveying device for introducing cement raw materials into the preheater system; wherein the cement raw materials include slag, having a particle size in a range from about 1 mm to about 5 cm and finely ground non-slag cement raw materials; and wherein the slag is selected from at least one member of the group consisting of steel slag, air cooled blast furnace slag, copper slag and zinc slag.
19. An apparatus according to claim 18, further comprising a pneumatic conveying device; wherein the mechanical conveying device introduces slag, having a particle size in a range from about 1 mm to about 5 cm, into the preheater system; and the pneumatic conveying device introduces finely ground non-slag cement raw materials into the feed end of the preheater system.
20. An apparatus according to claim 19, wherein the preheater system comprises a preheater equipped with a precalciner; wherein the mechanical conveying device introduces the slag into the precalciner. |
PROCESS OF MAKING CEMENT CLINKER
TECHNICAL FIELD
This invention relates to a process of manufacturing cement clinker, and more particularly, to a cement clinker manufacturing process that is carried out in a rotary kiln equipped with a preheater system.
BACKGROUND
Cement clinker is generally produced by the heat treatment, or pyroprocessing, of finely ground cement raw materials in a kiln. A finished cement, e.g., a Portland cement, may be manufactured from the cement clinker thus produced by subsequent milling and grinding steps.
The raw materials that are pyroprocessed to make cement clinker may include, for example, limestone, clay and sand. One typical clinker production process utilizes a rotary kiln. Finely ground cement raw materials are introduced into the feed end of the kiln. The rotary kiln is inclined so that, as the kiln rotates, the cement raw materials progress along the length of the kiln from the feed end to the output end.
As cement raw materials progress through the rotary kiln, they are exposed to a temperature gradient from about 100 0 C at the start of the process, up to about 1500 0 C at the hottest point of the rotary kiln. The initial processing, at temperatures from about 100 0 C to about 800 0 C, serves a variety of functions, including removal of moisture from the cement raw materials. This portion of the processing is often termed precalcining. As the material is further heated from about 800° C to about 1200° C, evolution of carbon dioxide occurs, e.g., associated with conversion of carbonates such as calcium carbonate and magnesium carbonate to calcium oxide and magnesium oxide respectively. This portion of the pyroprocessing is often termed calcining. The material is further heated from about 1200° to about 1500° in the so- called burning zone of the kiln, and this is where the final stages of clinker compound formation occur. The burning zone of the kiln is often subdivided into an upper transition zone, where both calcination processes and interim phase formations are occurring simultaneously; the sintering zone, where unstable interim phases exothermically transform into more stable compounds; and the cooling zone, where compounds that are partially liquid in the sintering zone are solidified.
There are at least two different types of rotary cement kilns. One type of rotary kiln is a conventional long, or elongated rotary kiln. In such a long kiln, the entire process of forming clinker occurs in the kiln. The kiln length corresponds to the requirements for completion of a process that begins with introduction of finely ground unprocessed cement raw materials into the feed end of the rotary kiln.
The other type of rotary kiln is one equipped with a preheater system, e.g., a preheater optionally equipped with a precalciner. Rotary kilns equipped with preheater systems differ significantly from conventional elongated rotary kilns. First, kilns equipped with a preheater system are significantly shorter in length than conventional long kilns. The difference in kiln length reflects a fundamental difference in the start-point for pyroprocessing in a rotary kiln equipped with a preheater system. In such systems, a substantial portion of the pyroprocessing, including all of the precalcining and most or all of the calcining portion, occurs in the preheater system, prior to the material entering the rotary kiln itself. The comparatively shorter kiln length thus relates to the fact that the clinker formation process occurring in the rotary kiln itself begins, not with unprocessed cement raw materials as in a conventional long kiln, but rather with cement raw materials that have already been processed by the preheater system.
The portion of the pyroprocessing that is performed in the preheater system is performed in a profoundly different way than the early portion of pyroprocessing accomplished in a conventional elongated rotary kiln. This is primarily because heat exchange is fundamentally different in a preheater than it is inside the rotary kiln itself. Inside an elongated rotary kiln, heat exchange is inefficient because hot gases heat only the surface of the moving bed of material. Conventional elongated kilns are generally fitted with a chain system at the back of the kiln to facilitate heat transfer.
In contrast, in a preheater system, the raw materials are in an air suspension, resulting in more immediate contact between the hot gases and the raw material particles. By one estimate, achieving 90% calcination in a conventional long rotary kiln requires the raw materials to travel about 45 meters of kiln length, and may require more than one hour of reaction time. See, Kurt E. Peray, "The Rotary Cement Kiln," Second edition, Chemical Publishing Co. Inc., 1986, the entire disclosure of which is incorporated herein by reference. In contrast, in a suspension preheater system,
achievement of the same 90% calcination of raw materials may be accomplished in less than a minute due to the higher heat transfer efficiency.
One kind of rotary kiln equipped with a preheater system is a "preheater kiln," wherein the preheater system comprises a preheater, such as for example a suspension preheater. Generally, in a preheater kiln, one or more cyclone-type preheater vessels are connected to the rotary kiln in the gas stream exiting the rotary kiln. Commonly, there is more than one of the cyclone-type preheater vessels. Multiple cyclones are typically arranged vertically in series, supported by a structure known as a preheater tower. Preheater kilns are also known as a suspension preheater kilns because the hot exhaust gases from the rotary kiln typically pass countercurrently through the downward moving raw materials in the preheater. The preheater tower is commonly configured with four preheater vessels at different heights in the tower, which are commonly referred to as stages, e.g., Stage 1, Stage 2, etc.
Another kind of rotary kiln equipped with a preheater system is a "precalciner kiln," wherein the preheater system comprises a preheater, such as for example a suspension preheater, which is equipped with a precalciner. A precalciner kiln is similar to a preheater kiln, and is also typically configured as a multistage preheater tower, most often a four stage preheater tower. However, the precalciner kiln is additionally provided with a precalciner which is typically attached to the lowest stage of the preheater tower. The precalciner typically has a secondary firing system which is independent of the firing system for the rotary kiln itself.
Slags have conventionally been a waste material from various metal production processes. Nonferrous slags are produced in a few locations, often remote from potential markets. As a result, they are not well utilized and most of the nonferrous slag produced is disposed of in slag dumps or stockpiles.
Steel slag, also known as converter slag, includes any type of slag produced during the manufacture of iron based alloys in an iron converter, an open hearth furnace, an electric arc furnace or a basic oxygen furnace. Steel slag is often produced at a steel mill in large, irregularly shaped chunks or pieces. Blast-furnace slag is a nonmetallic product, consisting essentially of silicates and aluminosilicates of calcium and other bases, that is developed in a molten condition simultaneously with iron in a blast furnace. Air-cooled blast furnace slag is the material resulting from solidification of molten blast-furnace slag under
atmospheric conditions: subsequent cooling may be accelerated by application of water to the solidified surface.
Nonferrous slags are produced during the recovery and processing of nonferrous metal from natural ores. The slags are molten by-products of high temperature processes that are primarily used to separate the metal and nonmetal constituents contained in a bulk ore. When molten slag is cooled, it converts to a rocklike or granular material. Copper and zinc slags are produced by: (1) roasting, in which sulfur in the ore is eliminated as sulfur dioxide (SO 2 ); (2) smelting, in which the roasted product is melted in a siliceous flux and the metal is reduced; and (3) converting, where the melt is desulfurized with lime flux, iron ore, or a basic slag and then oxygen lanced to remove other impurities.
Cement clinker production typically requires large amounts of energy and raw materials. Industrial byproducts such as slags can be used to replace a portion of the nonrenewable virgin raw materials such as limestone that are required for clinker production processes. Also, because slags have previously been processed at high temperature, there is a substantially lower energy requirement for the further pyroprocessing of the slag in the clinker formation process. For these reasons, blast furnace slag and steel slag have been employed in some cement production processes. Transformation of cement raw materials into cement clinker includes conversion of various metal carbonates to the corresponding metal oxides, thereby producing substantial emissions of carbon dioxide, a well known greenhouse gas. Employing slag as a portion of the cement raw materials can reduce carbon dioxide emissions because the previous processes that produced the slag have already converted most or all of the carbonates to the corresponding oxides. There is an increasing need to find new cement production processes that can improve energy efficiency, conserve nonrenewable raw materials and reduce greenhouse gas production. New processes that facilitate the incorporation of industrial byproducts, such as slags, into the raw materials used for cement clinker manufacture would thus be economically and environmentally invaluable.
SUMMARY
According to one aspect of the present invention, there is provided a process for producing cement clinker using a rotary cement kiln that is equipped with a preheater system, e.g., a preheater kiln or a precalciner kiln. The preheater system has
a feed end and an outlet end. The outlet end of the preheater system is communicably connected to the feed end of a rotary cement kiln. The process comprises introducing cement raw materials into the preheater system. The cement raw materials include slag having a particle size in the range from about 1 mm up to about 5 cm and non- slag cement raw materials. According to one embodiment of the process, the preheater system comprises a preheater, e.g., a suspension preheater. According to another embodiment of the process, the preheater system comprises a preheater equipped with a precalciner.
According to another embodiment of the invention, there is provided an apparatus for producing cement clinker. The apparatus comprises a rotary cement kiln that is equipped with a preheater system, and a mechanical conveying device for introducing cement raw materials into the preheater system. The cement raw materials include slag having a particle size in the range from about 1 mm up to about 5 cm and finely ground non-slag cement raw materials. According to one version of the invention, the preheater system comprises a preheater, e.g., a suspension preheater. According to another sub-embodiment of the invention, the preheater system comprises a preheater equipped with a precalciner.
The mechanical conveying device for introducing cement raw materials into the preheater system is, for example, a belt conveyer, a screw conveyer or a bucket elevator. In one version, the mechanical conveying device introduces the slag and the finely ground non-slag cement raw materials into the preheater system. In another version, the mechanical conveying device introduces the slag into the preheater, and a pneumatic conveying device introduces finely ground non-slag cement raw materials into the preheater system. In still another variation, the preheater system comprises a preheater equipped with a precalciner, and the mechanical conveying device introduces the slag into the precalciner, and the pneumatic conveying device introduces finely ground non-slag cement raw materials into the feed end of the preheater system. The rotary cement kiln employed in the process and apparatus of the invention is equipped with a preheater system and is accordingly other than a conventional long, or elongated rotary cement kiln.
The cement raw materials for use in the apparatus and process of the invention include both slag and non-slag cement raw materials. The slag component of the cement raw materials has a particle size from about 1 mm up to about 5 cm. The non-
slag cement raw materials are finely ground. The slag component of the cement raw materials is selected from at least one member of the group consisting of steel slag, air cooled blast furnace slag, copper slag and zinc slag.
The details of one or more embodiments of the invention are set forth in the accompanying drawings and the description below. Other features, objects, and advantages of the invention will be apparent from the description and drawings, and from the claims.
DESCMPTION OF DRAWINGS
FIG. Ia is a flowchart representation of one process according to the invention, in which slag having a particle size in the range from about 1 mm to about 5 cm and finely ground non-slag raw materials are both introduced into the feed end of a preheater and the output end of the preheater is connected to the feed end of a rotary kiln. FIG. Ib is a flowchart representation of another process according to the invention, in which finely ground non-slag raw materials are introduced into the feed end of a preheater and slag having a particle size in the range from about 1 mm to about 5 cm is introduced into the preheater at a point between the feed end and the output end, and the output end of the preheater is connected to the feed end of a rotary kiln.
FIG. 2 is a schematic drawing of a rotary cement kiln equipped with a preheater system, into which the cement raw materials, that include slag having a particle size in the range from about 1 mm to about 5 cm, are introduced.
FIG. 3 is a schematic drawing of a preheater kiln equipped with at least one conveying device for introducing slag, having a particle size from about 1 mm to about 5 cm into the preheater.
DETAILED DESCRIPTION
Preferred embodiments of the present invention and its advantages are best understood by referring to FIGS. Ia to 3 of the drawings, in which like numerals refer to like parts.
The flow charts in Figs. Ia and Ib illustrate two embodiments of the process of the invention. In Fig Ia, a rotary kiln 130 equipped with a preheater system 105 is used to prepare cement clinker from raw materials. The raw materials include slag that has a particle size in the range from about 1 mm to about 5 cm and finely ground non-slag cement raw materials.
According to FIG. Ia both the slag and non-slag components of the cement raw materials are introduced into the feed end of the preheater system. The non-slag portion of the cement raw materials is always added to the feed end of the preheater system. However, the slag component of the cement raw materials may be introduced into the preheater at any suitable entry port. The finely ground non-slag component may be introduced to the preheater using a variety of different conveying devices, e.g., a mechanical conveying device or a pneumatic conveying device. However, the slag component of the cement raw materials may be more suitably introduced into the preheater via a mechanical conveying device. Thus, for example, both the slag and non-slag components of the feed may be introduced into the feed end of the preheater system via a mechanical conveying device 150, such as a belt conveyer, a screw conveyer or a bucket elevator. Alternatively, slag having a particle size in the range from about 1 mm to about 5 cm may be introduced into to the feed end of the preheater system via a mechanical conveying device 150, and the finely ground non-slag component of the cement raw material is introduced into the feed end via a pneumatic conveying device 155. After processing by the preheater system, the processed materials move from the preheater system to the feed end 131 of the rotary kiln 130.
According to FIG. Ib, the slag component of the cement raw materials is introduced into the preheater system 105 via conveying device 160, at a point between the feed end and the output end, and the finely ground non-slag component of the cement raw materials is introduced into the feed end of the preheater system 105, via conveying device 165.
According to one embodiment, both conveying devices 160 and 165 are mechanical conveying devices such as belt conveyers, screw conveyers or bucket elevators. According to another embodiment, the conveying device 160 that carries the slag is a mechanical conveying device, and the conveying device 155 that carries the finely ground non-slag component of the cement raw material is a pneumatic
conveying device. After processing by the preheater system, the processed materials move to the feed end 131 of the rotary kiln 130.
When some or all of the cement raw materials are introduced into the preheater using a mechanical conveying device, the conveyer may be configured to reduce the amount of air introduced with the cement raw materials. For example, a belt conveyer may be equipped with a double tipping valve. Also, a screw conveyer may be operated in such a way that the screw conveyer, with the conveyed material contained therein provides an effective air seal.
FIG. 2 schematically illustrates an embodiment of the process of clinker formation using a preheater kiln 200. The preheater kiln comprises a preheater 205 and a rotary kiln 230. The preheater 205 optionally includes multiple stages. The preheater 205 in Fig. 2 is illustrated as including four stages, Stage 1, 210, Stage 2, 215, Stage 3, 220, and Stage 4, 225. The lowest stage of the preheater, illustrated in Fig. 2 as Stage 1 210, is communicably connected to the feed end 231 of the rotary kiln 230 such that materials processed by the preheater pass from the lowest stage of the preheater into the feed end of the rotary kiln.
Finely ground non-slag cement raw materials are introduced into the preheater 205 at the feed end 240, illustrated in Fig. 2 between Stage 3 220 and Stage 4 225. Slag, having a particle size in the range from about 1 mm to about 5 cm, is introduced into the preheater at one or more entry points, for example at the feed end 240 or at a point between the feed end and the output end 241 of the preheater 205. According to one embodiment of the invention, both the slag and non-slag components of the cement raw materials are introduced into the feed end 240 of the preheater. According to another embodiment of the invention, the slag component may be introduced into the lowest stage of the preheater 210.
Cement raw materials are conveyed to an entry point in the preheater by one or more conveying devices. According to one embodiment of the invention, the raw materials are conveyed to the feed end 240 of the preheater, via a mechanical conveying device 250, such as a belt conveyer, a screw conveyer or a bucket elevator. According to another embodiment, finely ground cement raw materials, other than slag, are conveyed to the feed end 240 of the preheater via a pneumatic conveying device 255, and slag raw materials are conveyed to the feed end 240 of the preheater, via a mechanical conveying device 250. According to another embodiment of the
invention, slag having a particle size in the range from about 1 mm to about 5 cm is introduced via a mechanical conveying device 250 to the lowest stage of the preheater, and finely ground non-slag cement raw materials are introduced into the feed end 240 of the preheater via a pneumatic conveying device 255. FIG. 3 schematically illustrates an embodiment of the process of clinker formation using a precalciner kiln 300. The precalciner kiln comprises a preheater system 305 and a rotary kiln 330, wherein the preheater system comprises a preheater 306 and a precalciner 335. The preheater 306 optionally includes multiple stages. The preheater 306, as illustrated in Fig. 3, has four stages: Stage 1, 310, Stage 2, 315, Stage 3, 320, and Stage 4, 325. The lowest stage of the preheater illustrated in Fig. 3 as Stage 1 310, is communicably connected to the feed end 331 of the rotary kiln 330 such that materials processed by the preheater system pass from the lowest stage of the preheater into the feed end of the rotary kiln. The precalciner 335 is attached to the lowest stage 310, and is equipped with a precalciner burner 345. Finely ground non-slag cement raw materials are introduced into the preheater at the feed end 340 of the preheater, illustrated in Fig. 3 between Stage 3 320 and Stage 4 325. Slag, having a particle size in the range from about 1 mm to about 5 cm, is introduced into the preheater at one or more entry points, for example at the feed end 440 of the preheater or into the precalciner 335. According to one embodiment of the invention, both the slag and non-slag components of the cement raw materials are introduced into the feed end 340 of the preheater. According to another embodiment of the invention, slag, having a particle size in the range from about 1 mm to about 5 cm, is introduced into the precalciner 335, and finely ground cement raw materials other than slag are introduced into the feed end 340 of the preheater. Slag that is introduced directly into the precalciner is introduced, for example with the fuel supplying the precalciner burner, or through a separate feed into the precalciner.
Cement raw materials are conveyed to the entry points in the preheater system by one or more conveying devices. According to one embodiment of the invention the raw materials are conveyed to the feed end 340 of the preheater via a mechanical conveying device 350 such as a belt conveyer, a screw conveyer or a bucket elevator. According to another embodiment, finely ground non-slag cement raw materials are conveyed to the feed end 340 of the preheater via a pneumatic conveying device 355, and slag raw materials are conveyed to the feed end 340 of the preheater, via a
mechanical conveying device 350. According to another embodiment of the invention, slag having a particle size in the range from about 1 mm to about 5 cm is introduced via a mechanical conveying device 350a or 350b to the precalciner 335, and finely ground non-slag cement raw materials are introduced into the feed end 340 of the preheater via a pneumatic conveying device 355. According to a sub- embodiment, the slag is introduced via a mechanical conveying device 350a into the precalciner through a separate feed. According to another sub-embodiment, the slag is introduced via a mechanical conveying device 350b into the precalciner through the same port used to feed fuel to the precalciner burner. The process and apparatus of the invention are not limited to the configurations exemplified in Figs. Ia to 3. For example, a cement manufacturing apparatus may be equipped with a double string preheater , optionally equipped with a precalciner, wherein one or more of the multiple stages of the preheater include more than one cyclone-type vessel. According to some embodiments of the process and apparatus of the invention, the slag component of the cement raw materials has a particle size from about 1 mm up to about 5 cm; or from about 1 mm up to about 4 cm; or from about 1 mm up to about 3 cm; or from about 1 mm up to about 2 cm; or from about 1 mm up to about 1 cm. According to other embodiments of the process and apparatus of the invention the slag component of the cement raw materials has a particle size from about 5 mm up to about 4 cm; or from about 5 mm up to about 3 cm; or from about 5 mm up to about 2 cm; or from about 5 mm up to about 1 cm. According to still other embodiments of the invention, the slag component of the cement raw materials has a particle size up to about 5 cm; or up to about 4 cm; or up to about 3 cm; or up to about 2 cm; or up to about 1 cm. Slag having particle sizes as described herein is produced, for example, by crushing and screening a slag material. No fine grinding, pulverizing or comminution of the slag component of the cement raw material is necessary for the process of the invention.
The non-slag component of the cement raw materials is preferably finely ground. Fine grinding of the non-slag component of the cement raw materials may be accomplished by use of a raw mill, e.g., a ball mill or any other method known in the art to produce finely ground cement rat materials. The expression "finely ground" is understood to indicate that the material has the consistency of fine powder, having an
average particle size less than about 100 microns. According to an embodiment of the invention the finely ground non-slag component of the cement raw materials has an average particle size less than about 75 microns. According to another embodiment of the invention, about 80% of the finely ground non-slag component of the cement raw materials passes through a 200-mesh screen.
A number of embodiments of the invention have been described. Nevertheless, it will be understood that various modifications may be made without departing from the spirit and scope of the invention. For example, the apparatus and process of the invention may be further equipped to modify, automatically or by action of an operator, the type, amount, and / or the entry point in the preheater system for the slag components of the cement raw material feed. Accordingly, other embodiments are within the scope of the following claims.