MXPA00005529A - Kiln plant and method for manufacturing cement - Google Patents

Abstract

The present invention relates to a kiln plant and a method for manufacturing cement. The kiln plant comprises a kiln for burning clinker, a cooler, a calciner followed by a separation cyclone and a burning compartment which is fed tangentially with tertiary air from the cooler. Completely or partially calcined material is routed from the bottom of the burning compartment to the calciner to which exhaust gases from kiln are also vented. The object of the invention is to provide a kiln plant and a method for manufacturing cement. The kiln plant is of a relatively simplified construction and it may advantageously burn fuel with a low reactivity, such as petcoke, anthracite and other grades of coal with a low gas content in the calcining zone. This object is obtained by locating the tangential inlet of the burning compartment so that the height of the upper part of the inner volume of the burning compartment, h1-h2, which is located below the burner tip and above the upper edge of the tangential inlet, is at least 1/3.D, where D is the diameter of that cylinder with the height h1-h2 and the same volume as the upper volume of the burning compartment, and that the height of the lower part of the inner volume of the burning compartment, h3-h4, being located between the lower edge of the tangential inlet and the outlet from the burning compartment, is at least D. Preferably, the height of the upper part of the inner volume of the burning compartment, h1-h2, should be at least 2/3.D and the height of the lower part of the inner volume of the burning compartment, h3-h4, should be at least D.

Description

CALCINATION PLANT AND METHOD FOR MANUFACTURING CEMENT DESCRIPTION OF THE INVENTION The present invention relates to a calcining plant and to a method for manufacturing cement.

The calcination plant comprises a kiln for calcining clinker, a cooler, a calciner followed by a cyclone separator and a precalcining compartment which is tangentially fed with tertiary air from the cooler. The whole or partially calcined material is sent from the bottom of the precalcining compartment to the calciner, to which the exhaust gases of the kiln are also evacuated. It is a recognized fact that a number of advantages can be obtained by constructing the calcination zone equipped with an additional pre-calcination compartment that is exclusively fed with tertiary cooler air. A plant of this kind is described in our patent EP-A-103423. For this patent a plant (SLC-S) for the calcination of cement raw materials is known in which the inherent difficulty in achieving a complete combustion of the fuel used in the calciner has been adequately taken into account. In this plant the raw material, after being preheated, is fed to a compartment (4) of precalcining in which it is calcined in hot air of the cooler (2). The tertiary air of the cooler flows centrally upwards through the bottom of the precalcining compartment (4), which means that in the precalciner compartment there is centrally an upward flow and a downward flow along the sides of the compartment. precalcining The raw material is fed by the lower end of the precalcining compartment and is distributed subject to the action of the turbulent flow that exists throughout the entire length of the precalcining compartment. From US-A-4, 014, 641 a plant for calcining cement raw materials is known in which the amount of nitrogen oxide in the exhaust gases of the furnace is reduced by generating a zone in the duct discharge of the furnace to which a reducing gas is fed. The hot air of the cooler and the hot air of the furnace are conducted respectively via a duct (5) and a duct (13) to a preheater cyclone (14, 15, 16, 17,) in which the raw material is preheated countercurrent of the hot gas from the cooler and the furnace. In the area of the kiln discharge duct located below the feed pipe (5) coming from the cooler, reducing conditions are generated by the introduction of reducing gases via a duct (12). The reducing gases are formed in the calciner (8) by virtue of which the volume of air that is fed to the calciner is sufficient to cause gasification of the fuel in the calciner but insufficient to cause a complete combustion of the fuel in the calciner (column 4). , lines 1-5). A disadvantage of this plant is that it is not possible to use fuels with difficult ignition and slow combustion such as petroleum coke, anthracite and other grades of coal with a low gas content, since they would produce a substantial amount of waste. unburned carbon that would precipitate and lead to the rotary kiln, subsequently causing problems in terms of sulfur ejection and the formation of agglutination. Another calcination system is known from US-A-5,364,265 in which the NOx emission is limited by the formation of reducing gases, specifically CO and H2 in a precalcining compartment (20). The coke that forms in the precalcining compartment during this process exhibits very distinctive properties. However, it is relatively difficult to optimize this method in terms of ensuring a minimum emission of NOx, since only very few can be controlled. parameters during the operation. The precalcining process in the precalcining compartment depends entirely on the degree of calcination desired for the raw material. At the same time the complexity of the structure of the plant is relatively high. Our method of reducing the NOx emission number of a plant is known from our international patent application No. PCT / DK 97/00029. The object of this invention is to provide a method of operation for a calcination plant with a reduced NOx emission rate while simultaneously providing the option of using a fuel with low reactivity, such as petroleum coke, anthracite and other grades of coal with low gas content in relatively low temperature zones. This object is achieved by regulating the fuel supply regimes in three different zones, feeding the exhaust gases from the other two zones into one zone in a way that ensures the minimization of the NO content in the exhaust gases of the area to which the exhaust gases of the other two zones are evacuated. The object of the present invention is to provide a calcining plant and a method for the manufacture of cement. The calcination plant is of relatively simplified construction and can conveniently burn low reactivity fuel, such as petroleum coke, anthracite and other grades of coal with low gas content in the calcination zone in which the temperature is usually found at a low level. According to the present invention there is provided a calcining plant for manufacturing cement, said plant comprising an oven, a cooler, a calciner with a subsequent cyclone separator, a precalcining compartment provided on its upper part with a central burner and below of the burner has a tangential inlet through which hot gas is fed from the cooler to the precalcining compartment via a duct in which an inlet for the raw powder is provided, a connection to the calciner being provided in the part of the precalcining compartment, and a second connection to the calciner directs to the latter the exhaust gases of the kiln; this plant is characterized in that the height hl-h2 of the upper part of the inner volume of the precalcining compartment, between the burner nozzle and the upper edge of the tangential inlet, which is the highest point of entry of the hot air of the cooler , is at least 1/3 D, where D represents the diameter of a cylinder having the height hl-h2 and the same volume as the upper part of the inner volume of the precalcining compartment; and in which the height h3-h4 of the lower part of the inner volume of the precalcining compartment which is located between the lower edge of the tangential inlet, which is the lowest point of entry of the hot air of the cooler, and the outlet of the compartment Therefore, if the precalcining compartment is cylindrical, this object is achieved by locating the tangential inlet of the precalcining compartment so that the height hl-h2 of the upper part of the internal volume of the precalciner compartment is located below the burner nozzle and above the upper edge of the tangential inlet is at least 1/3 D, and so the height h3-h4 of the lower part of the internal volume of the precalcining compartment, which it is located between the lower edge of the tangential inlet and the outlet of the precalcining compartment is at least D. Preferably the height h l-h2 of the upper part of the internal volume of the precalcining compartment should be at least 2/3 D and the height h3-h4 of the lower part of the internal volume of the pre-calcining compartment should be at least 3/2 D. This It will result that above the tangential entry of the suspension of raw material will generate a space with a high temperature and a low content of raw materials. This will ensure improved ignition and combustion characteristics for low-cost and gas-deficient carbon grades. This invention also includes a method for manufacturing cement in a plant according to the invention in which the raw materials are preheated and then subjected to at least a partial calcination in a precalcining compartment in the upper part of which a central burner is provided; wherein the raw materials are fed into the precalcining compartment via a tangential inlet suspended in the hot gas from a cooler; the partially calcined material is passed from the lower part of the precalcining compartment to a calciner via a connection, the gas / material suspension is passed from the calciner to a separating cyclone in which a separation of the gas and the material takes place, and where the exhaust gases of the furnace are directed to the calciner by way of a second pipeline, characterizing the method in which the height hl-h2 of the upper part of the internal volume of the precalcining compartment, between the burner nozzle and the edge The top of the tangential inlet, which is the highest inlet point of the hot gas of the cooler, is at least 1/3 D, with D being the diameter of a cylinder with the height hl-h2 and the same volume as the upper part of the internal volume of the precalcining compartment; and in which the height h3-h4 of the lower part of the internal volume of the precalcining compartment located between the lower edge of the tangential inlet, which is the lowest point of entry of the hot air of the cooler, and the outlet of the compartment (3 ) of precalcining is at least D. This invention will now be described in greater detail with reference to Figure 1 showing an example of a calcination plant according to the invention, and Figure 2 showing a detailed embodiment of the precalcining according to the invention. Figure 1 shows a calcining plant for manufacturing cement Clinker The plant is constituted by an oven 1 in which the clinker is heated to a temperature within the range of 1300-1500 ° C and a calciner 2 and a compartment 3 of precalcining in both of which the temperature is at least 800 ° C and in certain areas can be as high as 1400 ° C. In certain cases the calciner 2 can be constituted exclusively by the riser of the furnace 1. Next to the furnace 1 there is a cooler 4 of the clinker from which the hot air is conducted via a duct 5 to the calcination zone which is composed of 3, 2 and 8. The calciner 2 is fed with hot exhaust gases from the furnace 1 via the duct 6 and hot exhaust gases mixed with partially calcined material from the precalcining compartment 3 via a duct 7. From the calciner 2 the calcined material is conducted in suspension via a duct 8 to a cyclone 9 separator. In the cyclone 9 separator the gas / material suspension is separated into a stream of calcined material and a stream of hot gas. The calcined raw material is routed via the duct 10 to the rotary kiln 1 and the hot gas is routed via the duct 11 to a suspension preheater. The preheated raw material is directed down to the calcination zone via two ducts 14A and 14B. If deemed appropriate, the preheated raw material can also be fed to the upper part of the calciner 2 via a pipeline not shown. The duct 14B conducts the raw material into the interior (of the duct) of the exhaust gases of the furnace 1, causing the raw material to pass to the calciner 2. The duct 14A directs raw material into the interior of the tertiary air duct 5, causing the material is passed into pre-calcination compartment 3. The entire raw material jet is distributed in a controlled manner between the two ducts 14A and 14B, and in special circumstances it may, for example, be desirable to interrupt the flow through one of the ducts. In this plant it is possible to burn fuel in the calciner 2. by means of a burner 15, in the precalcining compartment 3 by a burner 16 and in the furnace 1 by a burner 17. Figure 2 shows a detailed embodiment of the compartment 3 of precalcining according to the invention, wherein the raw material of the duct 14A is introduced into the precalcining compartment 3 via the tertiary air duct 5. In this case the internal reaction volume of the precalcining compartment has a cylindrical shape. However, the shape of the upper volume of the reactor is not dictated by specific requirements except that the size of the area of the circular section must be sufficient in relation to the circular section of the burner in order to obtain the desired flow characteristics. The upper part of the internal volume of the precalcining compartment is that part which is located above the entrance of the tertiary air duct, and in figure 2 the height of this section is hl-h2. The height of the lower part of the internal volume of the precalcining compartment is h3-h4, and extends from the entrance of the tertiary air duct to the outlet which is located at the lower end of the precalcining compartment. Experience has shown that it is not possible to obtain the combination of high temperature, retention time and mixture that enhances the efficiency of the total combustion of the gas-deficient fuel that is introduced via the burner 16 but until hl-h2 is greater than 1/3 D, where D is the diameter of the upper section when it is cylindrical as in the previous case, and the lower part is greater than 3/2 D. When the raw powder feed pipe is located At the highest possible level in the precalciner compartment, which is the case in conventional plants, the basic consequence is that coal with a low content of volatile substances will not be burned in the upper third of the compartment, which means that the temperature maintains at a level around 800-900 ° C. On the other hand, the temperature at the outlet will rise due to the advanced state of calcination in this location. As a result, the outlet temperature can be as high as 1200 ° C, which can cause agglutination due to the raw powder content. Due to the low position in which the tertiary air inlet is placed, a mixing and ignition zone is generated in the upper part of the precalcining compartment that is free of raw raw material. The primary air jet through the burner generates the flow pattern illustrated in Figure 2, in which there is a vertical circulation in the central part of the precalcining compartment. Because the tertiary air of the cooler and the raw raw material suspended in the air stream are introduced tangentially, the raw raw material is thrown to the sides of the precalcining compartment by the turbulent action and, by virtue of which the circulation vertical takes place in the central part of the pre-calcination compartment the raw raw material content in the upper part of the pre-calcination compartment will be kept at a low level. The impact of the flow pattern will be to produce in the upper part of the precalcining compartment a gas mixture of which one will participate at this moment of time or in a previous stage in the combustion process and some of which will be gas containing oxygen (which comes) directly from the tertiary air duct. This mixture will trigger the ignition of the cold fuel that is introduced. It turned out that the consumption of coal in a precalciner compartment of an experimental plant could be reduced by a factor of about 17 percent after carrying out the method according to the present invention, and this probably must be attributed to an enhancement of the efficiency in the combustion of coal. Consequently, combustion in the precalcining compartment is always carried out with an oxygen content of less than 21 percent of 02. This has a beneficial effect on NOx production, which will be at a somewhat lower level. However, the most significant factor that influences the production of NOx is the increase in temperature. Accordingly, it was found that in a plant according to the invention, the conversion rate that can be achieved in terms of converting nitrogen from fuel to NOx will be as low as 25 percent when anthracite or petroleum coke is burned. In comparison, a traditional calciner can have a conversion rate as high as 65 percent for petroleum coke. This would indicate that the emission of NO in a plant according to the invention has been reduced by a factor of more than 50 percent.

Claims (9)

1. CLAIMS 1. Calcination plant to manufacture cement, being that the plant includes an oven, a cooler, a calciner with subsequent cyclone separator, a precalcining compartment provided in its upper part with a central burner and that below the burner has a tangential entrance through which hot gas is fed from the cooler to the pre-calcination compartment via a duct in which an inlet for raw material is provided; in the lower part of the precalcining compartment a connection is provided to the calciner and a second connection directs the exhaust gases from the kiln to the calciner, characterizing the plant because the height hl-h2 of the upper part of the internal volume of the precalcining compartment between the nozzle of the burner and the upper edge of the tangential inlet, which is the highest entry point of the hot gas of the cooler, is at least 1/3 D, where D means the diameter of a cylinder that has the height hl -h2 and the same volume as the upper part of the internal volume of the precalcining compartment; and because the height h3-h4 of the lower part of the internal volume of the precalcining compartment, located between the lower edge of the tangential inlet which is the lowest hot gas inlet point of the cooler and the outlet of the precalcining compartment, is at least D.
2. 2. Calcination plant for manufacturing cement according to claim 1 characterized in that the height hl-h2 of the upper part is at least 2/3 D.
3. 3. Calcination plant for manufacturing cement according to claim 1 characterized because the height h3-h4 of the lower part is at least 3/2 D.
4. Caulking plant for manufacturing cement according to claim 1, characterized in that the burner of the upper part of the precalcining compartment is arranged so that primary air is fed through the burner.
5. A method for manufacturing cement in a plant according to claim 1 in which the raw raw materials are preheated and then subjected to at least partial calcination in a pre-calcination compartment in the upper part of which a central burner is provided; wherein the raw raw materials are fed into the precalcining compartment suspended in hot gas from the cooler via a tangential inlet; the partially calcined material is passed from the lower part of the precalcining compartment to the calciner via a connection, the gas / material suspension is passed from the calciner to a separating cyclone in which the separation of the gas and the material is effected, and in which the exhaust gases from the furnace are conducted to the calciner via a second pipeline, the method being characterized by the fact that the height hl-h2 of the upper part of the internal volume of the precalcining compartment, between the burner nozzle and the upper edge of the tangential inlet which is the highest point of entry of the hot gas of the cooler is at least 1/3 D, where D is the diameter of a cylinder of height hl-h2 and the same volume as the upper part of the internal volume of the precalcining compartment; and by the fact that the height h3-h4 of the lower part of the internal volume of the precalcining compartment, which is located between the lower edge of the tangential inlet which is the lowest point of entry of the hot gas of the cooler and the outlet of the precalcining compartment is at least D.
6. 6. Method according to claim 4, characterized in that the temperature in the upper volume of the precalcining compartment is within the range of 1100-1400 ° C.
7. Method according to claim 4, characterized in that the temperature in the upper volume of the precalcining compartment is within the range of 1100-1400 ° C.
8. 8. Method according to claim 4, characterized in that primary air is fed to the precalcining compartment through the burner. Method according to claim 8, characterized in that the product of the percentage of primary air that is fed into the precalcining compartment with respect to the stoichiometric volume of air required to burn coal and the injection speed of the coal into the precalcining compartment measured in m / s, it is at least 500% * m / s.