MXPA99008174A - Method and burner for introducing fuel to a kiln - Google Patents

Abstract

A method as well as a burner are provided for introducing solid, liquid or gaseous fuel into the burning zone of a kiln, such as a rotary kiln for manufacturing cement clinker or similar products, where fuel is conducted through substantially concentric ducts (1, 6) and where primary air is conducted through two likewise concentric and annular ducts (8, 9) arranged around the fuel ducts, where the air in one of these air ducts (9) is made up of axially flowing air, whereas the air in the second air duct (8) comprises air which is caused to rotate about the centre axis of the burner, and where the portions of primary air can be independently controlled. The peculiar feature of the burner is that the primary airstreams are mixed at a relatively low velocity in a collecting duct (15) into a primary airstream which is subsequently accelerated up to a desired, relatively high velocity prior to being injected into the kiln via an annular nozzle (14). There is thus obtained effective mixing of fuel and air in an operationally reliable manner with a minimum loss of pressure, and the flame shape can be adapted to the optimum desired.

Description

METHOD AND BURNER TO INSERT FUEL TO AN OVEN DESCRIPTION OF THE INVENTION: The present invention relates to a method (referred to hereinbelow as of the kind described) for introducing solid, liquid or gaseous fuel into a burner zone of a furnace, such as a rotary kiln for making slag of cement or similar products, by which method the fuel is conducted through a duct or ducts and a primary air is conducted through at least two annular ducts arranged substantially concentrically with and around, the fuel ducts, the portion of air in one of the basically axially flowing air ducts, wherein the portion of air in the second of the air ducts comprises air having a rotating component about the center of the burner axis, and the amount of primary air in the two portions are controlled independently. The invention also relates to a burner for carrying out the method according to the invention. The burners for that purpose. They are well known. Originally they consist simply of a single tube through which a mixture of pulverized coal flour and air is injected into the burn zone of the furnace. Over time, the improvements in the design of the burners were made, with the incorporation of features such as additional ducts to introduce other types of liquid or gaseous fuel. In addition, more modern burners comprise one or more separate ducts for the injection of air, so that only a small amount of the primary air is injected together with the pulverized coal. By imparting a rotating motion to a part of the injected air it has been possible, to a large extent, to control the shape of the furnace flame. An example of a burner of the type mentioned is described in EP-B-0421903. This known burner comprises one or more ducts for the introduction of fuel, being surrounded by two annular ducts for injecting primary air. In the annular nozzle opening of the innermost of these ducts, oblique sheets are provided that impart a rotating movement to the air. The outermost duct air is driven and injected in a basically axial direction. An adjustment of the nozzle area of the two ducts can be made by adjusting the ducts axially to each other, and the primary air portions in the two ducts can be controlled independently. The variability in the. Therefore, with this burner, it is possible to adjust the flow rate and the velocity of the primary air as well as the amount of primary air that is subjected to the rotation. However, the disadvantage of this burner is that the primary air is injected through two separate annular nozzles, resulting in a relatively high pressure loss and less effective mixing of the primary air with the combustion in the burning zone. 'k - a second example of a burner ™ "the tip mentioned is described in EP-A-0650012. This burned also comprises one or several ducts for the introduction of fuel, surrounded by a single d d d primary discharge into an annular nozzle.

Immediately in front of the nozzle the air is directed through a number of flexible tubes causing the air 0 to rotate. The rotation of the air and thus the shape of the flame can be varied by changing the angle or bending of the tubes, and by changing the amount of primary air. The advantage of feeding all the primary air through only one nozzle reduces the loss of pressure and ensures an effective mixing of air and fuel, and therefore a continuous flame. However, the disadvantage of this type of burning is that the system with the flexible tubes requires a complex mechanism of regulation that also seems vulnerable in its intended operating environment. The purpose of the present invention is to provide a method as well as a burner by means of which effective fuel and air mixing is ensured with a minimum loss of pressure., and with which the shape of the flame can be varied, while simultaneously, the construction has a 5 degree of robustness that ensures a reasonable period of service, taking into account the high mechanical and thermal loads imposed on the burner in the area. of burning of a rotary kiln. This is achieved by means of a method of the kind described, characterized in that the two primary air parts are mixed at a lower speed in a collecting duct in a single stream of mixed primary air which is subsequently accelerated at a further discharge rate. elevate The invention also includes a burner for introducing solid, liquid or gaseous fuel into a burning zone of a furnace, such as a rotary kiln for making cement slag or similar products, a burner comprising a duct or ducts for driving the fuel and when minus two annular ducts arranged substantially concentrically with and around the fuel duct or ducts for driving primary air, the air ducts are arranged to cause the air portion in one of the ducts to flow axially and the air portion in the duct to flow axially. second air duct flows with a rotating component around the central axis of the burner, and means for independently controlling the amount of primary air in the parts, characterized in that the primary air ducts discharge into an annular joint of a collecting duct to conduct the primary air mixed to an annular nozzle, and because the flow area of the collecting duct decreases g radically in the axial direction of air movement. Thus a method as well as a burner is obtained by means of which effective mixing of fuel and air is achieved in an operationally reliable manner with a minimum of pressure loss, and with which the shape of the flame can be adapted to the desired optimum . This is due to the fact that the two substreams of the primary air, before they are injected into the furnace, mix at a relatively low speed in a stream of air which then has a high velocity, injected via a nozzle, the fact that the degree of rotation of the primary air can be varied by changing the inter-related amount of the two primary air streams, and the fact that all necessary control means can be installed in a fully accessible manner outside the burner zone of the furnace . As a result, those parts of the burner that are subjected to thermal loads can be manufactured in a simple and robust design. It is preferred that the flow area of the collecting duct from the location of the primary air streams is mixed to the annular nozzle by decreasing by a factor between 5 and 12 so that the velocity of the primary air stream is accelerated by an equivalent factor . In a particularly preferred embodiment of the burner according to the present invention, which is particularly suitable for application to a rotary kiln for making cement, it is preferred that the primary air ducts and the control means are arranged so that the axial velocity of the flow in the primary air ducts go between 20 and 25 m / s and in that the collector duct is arranged so that the primary air stream is accelerated up to a flow velocity of between 160 and 200 m / s. The collector duct can be configured in any practicable manner that of an acceleration corresponding to the aforementioned. However, it is preferred that the duct be made of two concentric annular elements, of which the outer one is configured as a truncated cone that is convergent in the direction of flow with an angle of inclination alpha between 30 and 60 °, with respect to the axis central of the burner, while the innermost annular element is basically parallel to the central axis of the burner. However other configurations of the collecting duct are conceivable. Thus the innermost annular element can also be configured as a truncated cone that is convergent in the direction of flow. Nevertheless, if this is the case, it must be formed with an angle of inclination that is considerably less than that of the outermost annular element. The air in the second air duct can be made to rotate about the central axis of the burner in different ways, among others by means of angularly rotated tubes as noted above. It is however preferred that the air be made to be carried by oblique sheets which are inserted in the second air duct immediately upstream of the discharge point of the duct. The ring nozzle should be configured in a way that ensures that pressure loss is minimized. It may also consist of two concentric annular elements, at least one of which is configured as a truncated cone so that the nozzle area may vary in an axial displacement of the two elements from each other. The invention will be described in detail with reference to the drawings, which are diagrams, and wherein: The Figure shows a section through the front section of the first embodiment of a burner according to the invention, FIG. front view of the same burner; Figures 2a, 2b, 2c and 2d show alternative modes of a primary air nozzle than a variable area; Figures 3a show a sectional view through the front section of a second embodiment of the burner according to the invention; Figure 3b presents a front view of the same burner. In Figures la and ib a burner is shown which is made to combine to burn an oil and pulverized coal, and which comprises a protective tube 2 in which a separate lance 1 is inserted to drive and atomize the fuel oil. Concentrically to the protective tube 2 there are two tubes 3 and 4 which between them form an annular duct 6 for driving and injecting a mixture of pulverized coal and air. In order to cool the oil burner and to keep it free of dust, a small amount of the primary total air can be conducted and injected into the space between the inner tube 3 and the protective tube 2. In addition to the protective tube 2 it is possible to insert one or several tubes in the inner tube 3 to introduce supplementary alternative fuels. Arranged concentrically around the tubes 2, 3 and 4 there is an air tube 5, which together with the carbon tube 4, forms an annular duct 8 for driving some of the primary air, called air with rotation. A number of oblique sheets 10 are fitted at the discharge end of the duct 8 in order to subject the rotating air to a rotary movement. Concentrically around the tube 5 a burner tube 7 is fitted which in conjunction with the radial air tube 5 forms an annular duct 9 for driving the shelf part of the primary air, called axial air. Since the temperature in the burning zone can be extremely high, the exterior of the burner tube 7 is provided with a ceramic refractory lining 11. According to the invention, the primary air ducts 8 and 9 discharge into an annular joint collector duct. 14. In the embodiment, the collecting duct is provided between the tube 4 and a cone-shaped annular element 7a which is connected to the burner tube 7. In the collecting duct , the primary air streams are mixed in an air stream which, due to the design of the collecting duct, is accelerated even before being injected into the combustion zone of the furnace through an annular nozzle opening 14. The nozzle opening 14 is provided between the outermost nozzle ring 12 which is fixed to the annular element 7a and an innermost nozzle ring 13 which is fixed to the carbon tube 4. By providing one or both nozzle rings 12, 13 with a surface conical, the area of the nozzle 14 can be varied by an axial displacement of the two nozzle rings relative to each other. Figures 2a, 2b, 2c and 2d show different options for configuring the nozzle 14. In Figure 2a the outer part 12 of the nozzle 14 is formed as a thin converging truncated cone, wherein the internal part 12 is made as a cylinder , the direction of the air flow is then adjusted slightly towards the center line of the burner. The nozzle 14 in Figure 2b is formed with a smooth circular opening wherein the innermost nozzle ring 13 is made with a divergent, thin truncated cone, which means that the direction of flow is adjusted slightly away from the center line of the burner. Examples of nozzles are shown in Figures 2c and 2d 14 which are configured so that the flow direction is axially aligned. In Figures 3a and 3b a burner is shown that does not incorporate a carbon tube 4. In this case the innermost nozzle ring is now fixed to the inner tube 3. The operating principle of the burner shown in Figures la and Ib is that the fuel oil is introduced and atomized by means of the burner lance 1. In order to cool the burner lance and keep it clean, a small amount of the primary air is injected into the space between the inner tube 3 and the protective tube 2 A mixture of pulverized coal and conveying air is injected through the annular duct 6. The primary air is introduced and distributed by known methods for example in FR-A-2348438, which is included by reference, to the two air ducts. primary 8 and 9. The quantities of air supplied to the two ducts 8 and 9 can be controlled independently of one another. In the collecting duct 15 the two primary air streams are mixed in an air stream, the flow characteristic of the mixed air stream is a resultant of the characteristics of the two intermixed air streams and comprises both axial and rotational components, whose inter-relation is variable by controlling the two primary air currents so that the optimum flame is reached. As previously mentioned, the primary mixed air stream in the collecting duct 15 is accelerated to a desired speed before being injected into the furnace through the annular nozzle 14. The pulverized coal and the transporting air must be injected into the furnace at a speed that is high enough to keep the carbon particles suspended, but not so high that the tubes are subjected to an unacceptable degree of wear, normally the speed should be between 25-40 m / s'. In cases where the burner is used in a conventional rotary kiln to manufacture, for example, cement slag, the amount of primary air to be injected through the burner will typically be between 5 and 15% of the combustion air that is require theoretically. The remaining combustion air, called secondary air, is introduced into the furnace without the burner entering the process. Frequently, the cooling air from a subsequent material cooler is used as secondary air, the cooling air is typically heated to a level around 1000 °. When the burner is used for such applications the injection speed of the primary air must be much higher than the fuel injection speed, normally it would be within the range of 160 to 200 m / s. When the primary air leaves the nozzle 14 it will carry with it the hot secondary air, mixing it with the fuel. Due to the high secondary air temperature of approximately 1000 °, the fuel will ignite. The shape of the flame that is of paramount importance in order to ensure a continuous production of cement slag can be altered by varying the primary air flow rate and the injection speed, and by varying the extent to which the air is subjected to in rotation. Normally, a modest degree of rotation of the air stream is required, and therefore. thus, the amount of primary air that is subjected to rotation as it is conducted through the duct 8 typically represents between 0 and 36 5 of the total primary air flow.

Claims (8)

1. - A method for introducing a solid, liquid or gaseous fuel into the combustion zone of an oven, such as a rotary kiln for manufacturing cement slag or similar products, by which method the fuel is conducted through a duct or ducts and the primary air is conducted through at least two annular ducts arranged substantially concentrically with and around the fuel duct or ducts, the portion of air in one of the air ducts that flows substantially axially while the portion of air in the other air duct comprises air having a rotating component around the central axis of the burner, and the amount of primary air in the two portions is controlled independently, characterized in that the two primary air portions are mixed at a low speed in a collector duct and a single mixed primary flow stream that subsequently accelerates at a higher discharge velocity, what is desired

2. A method according to claim 1, wherein the mixed primary air stream is accelerated by a factor of between 5 and 12.

3. A method according to claim 1 or 2, wherein the axial flow velocity of the primary air in two air ducts is between 20 and 25 m / s, and the mixed primary air stream is accelerated even at a speed of flow between 160 and 200 m / sec.

4. A method according to the preceding claims, wherein the air in the second air duct is forced to rotate about the central axis of the burner by directing it passing a number of oblique sheet sheets immediately upstream of the discharge end of the burner. pipeline.

5. A burner for introducing solid, liquid or gaseous fuel into a burning zone of an oven, such as a rotary kiln used to manufacture cement slag or similar products, a burner comprising a pipeline or ducts for driving the fuel and when minus two annular ducts arranged outside and concentrically with, and to the duct or fuel ducts to drive the primary air, the air ducts are arranged to drive a portion of air in one of the ducts to flow axially and the air portion in the second pipeline «of air flow with a rotating component around the central axis of the burner, and means for independently controlling the amount of primary air in the two portions, characterized in that the primary air ducts discharge into an annular seal collector duct for driving the primary air mixed to the annular nozzle and the flow area of the collecting duct gradually decreases in the axial direction of the movement. air.

6. - A burner according to claim 5, wherein the flow area of the collecting duct decreases by a factor of between 5 and 12.

7. - A burner according to claim 5 or 6, wherein the ducts of Primary air and control means are arranged so that the axial flow velocity in the primary air ducts is between 20 and 25 m / s and the collecting duct is arranged so that the mixed primary air stream is accelerated to a speed of flow between 160 and 200 m / sec.

8. A burner according to claim 7, wherein the collecting duct is made of two concentric annular elements, of which the outermost element is configured as a truncated cone that is convergent in the direction of flow with an angle of inclination between 30 and 60 ° with respect to the central axis of the burner.