Method for operating a combustible waste injection device

Abstract

To provide a combustible waste injection apparatus capable of being attached to a rotary kiln for producing cement that can reduce the amount of hexavalent chromium contained in the cement as well as suppressing impact on cement quality while the amount of input chromium and operating conditions of the rotary kiln are the same as before.SOLUTION: The combustible waste injection apparatus that is attachable to the rotary kiln for cement production having a first burner through which a main fuel is injected, comprises a second burner different from the first burner, through which combustible waste is injected. The second burner is arranged so that an axis of the second burner is positioned within a region sandwiched between a first position vertically below the axis of the first burner as seen from an extension direction of the first burner, and a second position at 170° in a direction opposite to a rotation direction of the rotary kiln from the first position based on the axis.SELECTED DRAWING: Figure 4

Description

[Technical Field]

[0001] The present invention relates to a combustible waste injection device that can be attached to a rotary kiln for producing cement, and a method for operating the same. [Background technology]

[0002] Cement is produced by burning raw clinker materials with fuel in a rotary kiln. These raw clinker materials contain chromium, most of which exists in the form of trivalent chromium.

[0003] When trivalent chromium is oxidized and fired during the cement manufacturing process, part of it is oxidized to hexavalent chromium. Hexavalent chromium is more soluble in water than trivalent chromium and is known to be harmful to the human body. For this reason, it is necessary to reduce the amount of hexavalent chromium contained in cement when manufacturing cement.

[0004] To reduce the amount of hexavalent chromium in cement, two methods are considered: reducing the amount of chromium fed into the rotary kiln (i.e., the input chromium amount) and reducing the conversion rate from trivalent chromium to hexavalent chromium. However, the former method limits the materials that can be used as clinker raw materials, which inhibits the trend toward treating and recycling various waste materials. On the other hand, the latter method requires controlling factors such as the flame condition during combustion, the amount of oxygen, and the components of the clinker raw materials to prevent the clinker from being burned in an excessively oxidizing state. However, because the environment during clinker burning in a rotary kiln is determined by the complex interactions of these factors, it is not easy to create an appropriate burning environment while controlling these factors.

[0005] Under these circumstances, a technology is known in which oil coke, which is more flame-retardant than pulverized coal, the main fuel, is injected near the kiln burner (main burner) and dropped onto the clinker to reduce and burn the clinker (see, for example, Patent Document 1 below). [Prior art documents] [Patent documents]

[0006] [Patent Document 1] Japanese Patent Application Publication No. 11-189442 Summary of the Invention [Problem to be solved by the invention]

[0007] However, the combustion rate of oil coke is extremely slow compared to pulverized coal, and it takes a long time for it to completely burn. As a result, there is a concern that unburned oil coke may remain in the clinker and be discharged from the clinker cooler, affecting the quality of the cement. In addition, because oil coke is a valuable commodity, there is also the disadvantage of increasing the cost of cement production.

[0008] In view of the above problems, an object of the present invention is to provide a combustible waste injection device that can be attached to a rotary kiln used for cement production, and an operating method thereof, which can reduce the amount of hexavalent chromium contained in cement while maintaining the input chromium amount and rotary kiln operating conditions from conventional levels and suppressing the impact on cement quality. [Means for solving the problem]

[0009] The combustible waste injection device according to the present invention can be attached to a rotary kiln for producing cement, the rotary kiln including a first burner into which a primary fuel is injected, the device comprising: a second burner that is different from the first burner and that blows combustible waste into the combustion chamber; The second burner is characterized in that, when viewed in the blowing direction of the first burner, the axis of the second burner is positioned within an area sandwiched between a first position vertically below the axis of the first burner and a second position 170° forward from the first position in the opposite direction to the rotation direction of the rotary kiln, based on the axis.

[0010] Cement clinker (hereinafter referred to as "clinker") burned in a rotary kiln falls toward a clinker cooler for cooling. A clinker cooler is a device into which air, usually at room temperature, is blown in and exchanges heat with the clinker, which is at 1000°C or higher (typically about 1350°C), to cool the clinker. After heat exchange in the clinker cooler, the air flows into the rotary kiln and is used as secondary air. This secondary air swirls around the rotary kiln. The temperature of this secondary air is typically about 800°C to 900°C.

[0011] In other words, the secondary air flowing from the clinker cooler into the rotary kiln enters the rotary kiln while swirling in the same direction as the rotation of the rotary kiln.

[0012] On the other hand, a rotary kiln is a long tubular body (body) that slopes downward at a slight angle (typically about 2°) toward the clinker cooler, and is a device that burns the clinker (clinker raw material) inside while rotating.Due to the rotation of the rotary kiln and friction between the clinker and the inner wall of the rotary kiln, the clinker during burning remains on a slope that is biased toward the rotation direction of the kiln rather than on the vertically downward bottom surface of the rotary kiln.

[0013] In the above-described combustible waste injection device, the second burner through which combustible waste is injected is positioned so that its axis is located within a region between a first position vertically below the axis of the first burner (main burner) and a second position 170° from the first position in the opposite direction to the rotation direction of the rotary kiln, as viewed from the extension direction of the first burner (main burner). In other words, when combustible waste is injected into the rotary kiln from the second burner installed at this position, the combustible waste is injected into the rotary kiln in a direction perpendicular to both the vertical and axial directions, opposite to the region where the clinker is being fired. This region corresponds to the region where the secondary air flows downward due to the rotation of the rotary kiln.

[0014] As a result, the injected combustible waste is likely to fall into the area where the clinker is being burned, following the downward flow of secondary air. When combustible waste lands on the clinker and burns, oxygen is removed from the vicinity of the clinker, creating a reducing atmosphere around the clinker during burning. This suppresses the oxidation of trivalent chromium, even when the clinker raw material contains trivalent chromium, and reduces the amount of hexavalent chromium produced. Therefore, the amount of hexavalent chromium contained in cement can be reduced without reducing the amount of input chromium compared to conventional methods.

[0015] The blowing direction of the first burner is essentially the extension direction of the first burner, and may refer to the direction from the kiln front side toward the kiln rear side.

[0016] The above-mentioned combustible waste injection device is a device in which the position of the burner (second burner) for injecting combustible waste is intentionally adjusted so that the combustible waste can be injected into the rotary kiln on the side opposite to the bottom where the clinker remains. Therefore, when it is necessary to reduce the amount of hexavalent chromium contained in cement, it is sufficient to simply inject combustible waste from the second burner with a predetermined amount of heat, and there is no need to significantly change the operating conditions of the rotary kiln from conventional ones.

[0017] Furthermore, since combustible waste is injected from the second burner, there is less risk of unburned material remaining in the clinker compared to when petroleum coke is injected. From this perspective, the combustible waste injected from the second burner is preferably combustible municipal or industrial waste that is primarily composed of one or more organic materials belonging to the group consisting of waste plastics, wood chips, ASR, waste tires, meat and bone meal, and biomass.

[0018] In this specification, "biomass" refers to organic resources derived from living organisms that can be used as fuel, excluding fossil fuels, and includes, for example, crushed waste tatami mats, crushed construction waste wood, wood flour, and sawdust.

[0019] The combustible waste blown in from the second burner preferably has a passing rate of 80% by mass or more through a 40 mm sieve, more preferably 85% by mass or more, and particularly preferably 90% by mass or more. If the combustible waste has a high proportion of particle sizes of 40 mm or less, there is an extremely high possibility that the clinker can be completely burned before it falls into the clinker cooler.

[0020] The combustible waste blown in from the second burner preferably has a heat distortion temperature of less than 100°C when the resin content is 60% by mass or more. In the case of combustible waste with a heat distortion temperature of 100°C or more, there is a possibility that it will not burn completely after being blown in and landing in the clinker, and some of it may remain unburned. Note that the heat distortion temperature of general-purpose plastics is less than 100°C.

[0021] On the other hand, when the resin content of the combustible waste fed from the second burner is less than 60% by mass, the fuel ratio is preferably 1.0 or less. Note that the "fuel ratio" here refers to the mass ratio of fixed carbon to volatile matter, and the smaller this value, the more flammable the material is.

[0022] The second burner may be arranged so that, when viewed in the blowing direction of the first burner, the axis of the second burner is located vertically below a horizontal plane passing through the axis of the first burner.

[0023] According to the above configuration, the floating time of the combustible waste can be shortened, so that a higher proportion of the combustible waste can land in the clinker.

[0024] The first burner and the second burner are fixedly attached to a downstream end surface of a kiln hood connected to the downstream side of the rotary kiln, When viewed from a direction parallel to the horizontal plane and perpendicular to the blowing direction of the first burner, the position of the tip of the second burner may be closer to the downstream end face of the kiln hood than the midpoint between an imaginary boundary plane parallel to the vertical direction connecting the rotary kiln and the kiln hood and the downstream end face of the kiln hood.

[0025] According to the above configuration, the floating time of the combustible waste can be shortened, and therefore a higher percentage of the combustible waste can land on the clinker. Furthermore, if the tip of the second burner is positioned too close to the virtual boundary surface, the length of the second burner located above the clinker cooler increases, which may block the flow of secondary air from the clinker cooler and increase the pressure loss within the rotary kiln. Furthermore, the area of ​​the outer surface of the second burner exposed to the high-temperature secondary air increases, which may cause thermal damage to the second burner. Furthermore, the longer length of the second burner increases the manufacturing cost of the entire device.

[0026] When the combustible waste injection device is operated, the second burner may blow the combustible waste into the rotary kiln at a wind speed of 20 m / s to 80 m / s.

[0027] If the wind speed is below 20 m / s, there is a concern that combustible waste may clog the piping of the second burner, while if the wind speed is above 80 m / s, the amount of cold air blown into the rotary kiln from the second burner increases, which may reduce the combustion efficiency inside the rotary kiln.

[0028] The second burner may be configured to blow the combustible waste toward the rotary kiln with a heat amount less than that input from the first burner.

[0029] Because there is an appropriate range of heat consumption rate from the viewpoint of clinker quality, if the heat input from the second burner is too high, it becomes necessary to reduce the heat input from the first burner (main burner). Such operation may significantly change the thermal history of the clinker, which may affect the quality of the clinker. From this viewpoint, the heat input from the second burner is preferably less than 50% of the heat input from the first burner, and more preferably less than 30%. Typically, the heat input from the second burner is about 10% or less of the heat input from the first burner.

[0030] In the method for operating the combustible waste injection device, a detection value of the total hexavalent chromium or water-soluble hexavalent chromium contained in the cement clinker extracted from the clinker cooler may be monitored, and when the detection value exceeds a predetermined value, control may be performed to increase the amount of the combustible waste injected from the second burner.

[0031] As an example, clinker extracted from a clinker cooler is dissolved in acid at intervals of, for example, 30 minutes to 1 day, and the hexavalent chromium concentration in the solution is measured by one or more methods from the group consisting of diphenylcarbazide absorptiometry, flame atomic absorption spectrometry, electrothermal atomic absorption spectrometry, ICP atomic emission spectrometry, ICP mass spectrometry, and flow analysis using diphenylcarbazide color development, as described in JIS K 0102:2016 "Testing Methods for Industrial Wastewater," to determine the total amount of hexavalent chromium contained in the clinker. As another method, the clinker is immersed in water, and the hexavalent chromium concentration in the solution into which the hexavalent chromium has eluted is measured using the above-mentioned method to determine the amount of water-soluble hexavalent chromium.

[0032] If the determined hexavalent chromium value exceeds a predetermined standard value, the amount of combustible waste blown into the second burner is increased, thereby increasing the proportion of the clinker that is reduced and burning, thereby reducing the hexavalent chromium content.

[0033] As described above, when the amount of combustible waste to be injected is adjusted according to the amount of hexavalent chromium determined using clinker extracted from the clinker cooler, a time lag occurs before clinker with a reduced hexavalent chromium content is obtained. However, the produced clinker is then stored in a large-capacity tank (clinker silo) for a certain period of time, and this storage tank functions as a buffer. Therefore, the above control method makes it possible to reduce the hexavalent chromium content in the cement obtained as a product. [Effects of the Invention]

[0034] By using the combustible waste injection device of the present invention, it is possible to reduce the amount of hexavalent chromium contained in cement while maintaining the input chromium amount and the operating conditions of the rotary kiln from conventional levels and suppressing the effects on cement quality. [Brief explanation of the drawings]

[0035] [Figure 1] 1 is a cross-sectional view schematically showing an embodiment of the combustible waste injection device of the present invention attached to a rotary kiln. FIG. [Figure 2] FIG. 1 is a schematic plan view of a rotary kiln viewed from the kiln hood side. [Figure 3] 3 is a diagram schematically illustrating only some of the elements extracted from FIG. 2. [Figure 4] 1 is a diagram showing a schematic diagram of the relationship between the installation positions of the first burner and the second burner when the rotary kiln is viewed from the downstream end face of the kiln hood. [Figure 5] This is a drawing in which the assumed area where the axis of the second burner is located is superimposed on Figure 4. [Figure 6] This is a drawing showing some elements extracted from Figure 1. [Figure 7A] FIG. 2 is a schematic cross-sectional view illustrating the dimensions and shapes of the rotary kiln, kiln hood, and first burner used in the simulation. [Figure 7B]FIG. 7B is a cross-sectional view taken along line BB in FIG. 7A. [Figure 7C] FIG. 7B is a cross-sectional view taken along line CC in FIG. 7A. [Figure 8] 10 is a diagram for explaining the position of the axis of the second burner verified by simulation. [Figure 9] 10 is a graph showing the particle size distribution of combustible waste RF1 assumed in the simulation. [Figure 10] 10 is a diagram showing an example of a simulation result. [Figure 11] Based on the results of Figure 10, the falling position of the fallen waste plastic was analyzed and graphed with the distance from the clinker drop hole on the horizontal axis and the amount of fallen waste plastic on the vertical axis. DETAILED DESCRIPTION OF THE INVENTION

[0036] Hereinafter, an embodiment of a combustible waste injection device and an operating method thereof according to the present invention will be described with reference to the drawings. Note that the drawings are schematic illustrations, and the dimensional ratios in the drawings do not necessarily correspond to the actual dimensional ratios. Furthermore, the dimensional ratios between the drawings do not necessarily correspond to each other.

[0037] 1 is a cross-sectional view showing a part of a cement production facility 1 (hereinafter abbreviated as "facility 1") in which an embodiment of the combustible waste injection device of the present invention is attached to a rotary kiln. The cement production facility 1 includes a rotary kiln 2 and a kiln hood 4 connected to the rotary kiln 2.

[0038] The rotary kiln 2 is a device that produces cement clinker (hereinafter referred to as "clinker 5") by burning clinker raw materials. Typically, the clinker raw materials are calcined via a preheater (not shown) installed upstream and flow into the kiln's base. The rotary kiln 2 has a horizontal cylindrical shape that is slightly inclined downward toward the downstream side (toward the kiln hood 4), and burns the clinker raw materials (or partially burned clinker) while rotating.

[0039] The upstream side of the kiln hood 4 is connected to the downstream end of the rotary kiln 2 and surrounds the downstream end of the rotary kiln 2. The lower side of the kiln hood 4 is connected to the clinker cooler 3. A first burner 10 and a second burner 20 are fixed to the downstream end face 4a of the kiln hood 4. A portion of the downstream end face 4a of the kiln hood 4 is typically in the form of an openable door, which is opened when repairing the rotary kiln 2 or installing or replacing the first burner 10 and the second burner 20.

[0040] The clinker raw material descending inside the rotary kiln 2 is burned by a first burner 10 and a second burner 20 attached to the kiln hood 4. After burning, the clinker 5 falls toward the clinker cooler 3 disposed below the kiln hood 4 and is cooled in the clinker cooler 3.

[0041] The temperature of the burned clinker 5 is 1000°C or higher, typically about 1200°C to 1500°C. This clinker 5 is cooled by ambient air A1 at room temperature (about 20°C to 30°C) that is blown in from a cooling fan (not shown) connected to the clinker cooler 3. The cooled clinker 5 is discharged from the outlet end of the clinker cooler 3 and stored in a clinker silo (not shown).

[0042] The air A1 that flows into the clinker cooler 3 exchanges heat with the high-temperature clinker 5, and is then supplied as secondary air A2 into the rotary kiln 2. This secondary air A2 is used as combustion air in the first burner 10 and the second burner 20.

[0043] In the following description, an XYZ coordinate system will be referred to where appropriate, in which the vertical direction is the Z direction, the axial direction on the kiln hood 4 side of the rotary kiln 2 is the X direction, and the direction perpendicular to the X and Z directions is the Y direction. In the following description, when a positive or negative direction needs to be distinguished, it will be written as "+X direction" or "-X direction," while when a positive or negative direction is not distinguished, it will be simply written as "X direction." The same applies to the Y and Z directions.

[0044] As described above, the clinker raw materials become clinker 5 during the process of being burned in the rotary kiln 2. In other words, depending on the location in the rotary kiln 2, materials existing in the form of clinker raw materials and materials existing in the form of clinker 5 will be mixed. In the following, for the sake of simplifying terminology, the clinker raw materials and clinker being burned in the rotary kiln 2 will be collectively referred to as "clinker 5."

[0045] FIG. 2 is a schematic plan view of the equipment 1 when the rotary kiln 2 is viewed from the kiln hood 4 side, i.e., in the +X direction. As described above, the rotary kiln 2 has a horizontal cylindrical shape that slopes slightly downward toward the downstream side (kiln hood 4 side). Therefore, conversely, when the rotary kiln 2 is viewed from the downstream side (kiln hood 4 side) toward the upstream side, i.e., in the +X direction, it has a slight upward slope. Therefore, when the rotary kiln 2 is viewed from the kiln hood 4 side, the position of the top of the cylindrical shape would normally be displaced in the Z direction. However, for convenience of illustration, only the portion of the rotary kiln 2 closest to the kiln hood 4 is shown in FIG. 2.

[0046] As described above, the rotary kiln 2 burns the clinker 5 inside while rotating. In the example of Figure 2, it is assumed that the rotation direction dr2 of the rotary kiln 2 is clockwise when viewed from the downstream side to the upstream side. In other words, the rotary kiln 2 burns the clinker 5 while rotating clockwise around the central axis 2c when viewed in the +X direction.

[0047] During burning, the clinker 5 remains on a slope that is biased in the rotation direction dr2 from the vertically lower bottom surface of the rotary kiln 2 due to the rotation of the rotary kiln 2 and friction between the clinker 5 and the inner wall 2a of the rotary kiln 2. As a result, the Y coordinate y2 of the axis 2c of the rotary kiln 2 and the Y coordinate y3 of the center of the area occupied by the clinker 5 that remains on the inner wall 2a of the rotary kiln 2 are displaced in the Y direction.

[0048] More specifically, y3 deviates from y2 as a reference in the direction of movement associated with the rotation of the rotary kiln 2 at a position vertically below (toward the -Z side) the axis 2c of the rotary kiln 2. In other words, when the rotation direction dr2 of the rotary kiln 2 is clockwise, y3 moves in the +Y direction at a position vertically below (toward the -Z side) the axis 2c of the rotary kiln 2, so y3 deviates from y2 in the +Y direction. Conversely, when the rotation direction dr2 of the rotary kiln 2 is counterclockwise, y3 moves in the -Y direction at a position vertically below (toward the -Z side) the axis 2c of the rotary kiln 2, so y3 deviates from y2 in the -Y direction.

[0049] As described above, the clinker cooler 3 is a device that cools the clinker 5 that has completed burning in the rotary kiln 2 by the atmosphere A1 (cooling air) from below. The clinker 5 that has moved to the downstream end of the rotary kiln 2 (clinker outlet 6: see Figure 1) falls through the hollow space in the kiln hood 4 toward the clinker cooler 3 below.

[0050] From the viewpoint of improving cooling efficiency, it is preferable to install the position of the center 3c of the clinker cooler 3 vertically below the center position of the area occupied by the clinker 5 during burning that remains on the inner wall 2a of the rotary kiln 2. In other words, the Y coordinate of the center 3c of the clinker cooler 3 approximately coincides with the Y coordinate (y3) of the center position of the area occupied by the clinker 5 during burning that remains on the inner wall 2a of the rotary kiln 2. As a result, the position of the center 3c of the clinker cooler 3 is shifted in the Y direction from the position of the axis 2c of the rotary kiln 2.

[0051] Figure 3 is a diagram that schematically illustrates only some of the elements extracted from Figure 2. As described above, the air A1 that flows into the clinker cooler 3 is heat exchanged with the high-temperature clinker 5, and then supplied as secondary air A2 into the rotary kiln 2 to be used as combustion air. In Figure 3, the flow of this secondary air A2 is schematically illustrated by a dashed line.

[0052] As described above with reference to Figure 2, the center 3c of the clinker cooler 3 is offset in the Y direction from the axial center 2c of the rotary kiln 2. The direction of the offset of the center 3c of the clinker cooler 3 relative to the axial center 2c of the rotary kiln 2 is the direction in which the center 3c moves in association with the rotation (rotation direction dr2) of the rotary kiln 2 at a position vertically below (on the -Z side of) the axial center 2c of the rotary kiln 2. Conversely, this direction is the direction in which the center 3c of the clinker cooler 3 moves closer to the axial center 2c as the rotary kiln 2 rotates at a position vertically above (on the +Z side of) the axial center 2c of the rotary kiln 2.

[0053] As shown in Figure 3, the secondary air A2 flowing into the rotary kiln 2 from the clinker cooler 3 side rises to a height position (Z coordinate position) at approximately the same height as the axis 2c of the rotary kiln 2, then continues to rise while swirling in the same direction as the rotation direction dr2 of the rotary kiln 2, and then exhibits an air flow that descends.

[0054] As shown in FIG. 1, a first burner 10 and a second burner 20 are attached to the kiln hood 4 and face the rotary kiln 2. The first burner 10 is a burner that injects the main fuel (pulverized coal) C1 into the rotary kiln 2. The second burner 20 is a burner that injects combustible waste RF1 into the rotary kiln 2 as an auxiliary fuel other than the main fuel. The combustible waste RF1 injected from the second burner 20 is preferably a material that is more flammable than oil coke. As an example, the combustible waste RF1 injected from the second burner 20 is general waste or industrial waste that is primarily composed of one or more organic materials belonging to the group consisting of waste plastics, wood chips, ASR, waste tires, meat and bone meal, and biomass, and that is combustible.

[0055] The inner diameter of the tube of the second burner 20 used to inject the combustible waste RF1 is preferably 100 mm to 300 mm. If the inner diameter is less than 100 mm, there is a possibility that some of the combustible waste RF1 will become clogged inside the tube. On the other hand, if the inner diameter is greater than 300 mm, the amount of air blown into the rotary kiln 2 together with the combustible waste RF1 will be excessive, which may affect the combustion environment inside the rotary kiln 2.

[0056] The location where the second burner 20 is attached in the equipment 1 of this embodiment will be described with reference to Fig. 4. Fig. 4 is a diagram that schematically shows the relationship between the installation positions of the first burner 10 and the second burner 20 when the rotary kiln 2 is viewed from the downstream end face 4a of the kiln hood 4. That is, Fig. 4 is a diagram that shows the relationship between the installation positions of the first burner 10 and the second burner 20 when viewed in the blowing direction of the first burner 10.

[0057] In the equipment 1 of this embodiment, the axis of the second burner 20 is located within the hatched area PA in Fig. 4. That is, the axis of the second burner 20 is located within the area PA between a first position ya1 vertically below the axis 10c of the first burner 10 and a second position ya2 170° forward from the first position ya1 in the direction opposite to the rotation direction dr2 of the rotary kiln 2 (counterclockwise in this case) with respect to the axis 10c.

[0058] The effect of positioning the axis of the second burner 20 at such a position will be described with reference to Fig. 5. Fig. 5 is a diagram in which the hatched area PA in Fig. 4 is superimposed on a diagram displayed according to Fig. 3.

[0059] As described above with reference to Figure 3, the secondary air A2 flowing from the clinker cooler 3 side toward the rotary kiln 2 rises to a height position (Z coordinate position) approximately the same as the axis 2c of the rotary kiln 2, then continues to rise while circling in the same direction as the rotation direction dr2 of the rotary kiln 2, and then descends.

[0060] In other words, the area PA where the axis of the second burner 20 is located corresponds to the area where the airflow of the secondary air A2 exhibits a downward airflow. Therefore, when the combustible waste RF1 is blown into the area PA, the combustible waste RF1 is unlikely to float and move within the rotary kiln 2 and is likely to fall toward the bottom of the rotary kiln 2 in a relatively short time. As a result, the combustible waste RF1 is more likely to fall toward the bottom of the rotary kiln 2 before being completely burned.

[0061] Clinker 5 being burned is present on the bottom surface of the rotary kiln 2. That is, when combustible waste RF1 before being burned, i.e., during combustion, falls toward the bottom surface of the rotary kiln 2, some of it lands on the surface of the clinker 5 being burned. If combustion continues with the combustible waste RF1 landing on the clinker 5, oxygen is taken away from the vicinity of the clinker 5 as a result of this combustion, and the clinker 5 being burned becomes a reducing atmosphere. As a result, even if the clinker raw material contains trivalent chromium, oxidation of trivalent chromium during burning in the rotary kiln 2 is suppressed, and the amount of hexavalent chromium produced can be reduced.

[0062] Whether or not to inject the combustible waste RF1 from the second burner 20, and the amount of heat to be input if injected, may be determined according to the analysis results of the clinker 5 discharged from the clinker cooler 3. If the analysis results exceed a predetermined reference value, a process of injecting the combustible waste RF1 from the second burner 20 is performed. A specific analysis interval is, for example, 30 minutes to 1 day.

[0063] Specifically, to measure total hexavalent chromium in clinker, clinker 5 discharged from clinker cooler 3 is ground into a fine powder and dissolved in a 2x diluted (1+1) hydrochloric acid solution. The hexavalent chromium concentration in the solution is determined by one or more of the following methods, as specified in JIS K 0102:2016 "Testing Methods for Industrial Wastewater," namely, diphenylcarbazide absorptiometry, flame atomic absorption spectrometry, electrothermal atomic absorption spectrometry, inductively coupled plasma (ICP) atomic emission spectrometry, inductively coupled plasma (ICP) mass spectrometry, and flow analysis using diphenylcarbazide color development, using a standard addition calibration curve. To measure water-soluble hexavalent chromium in clinker, clinker 5 discharged from clinker cooler 3 is ground into a fine powder and analyzed using JCAS I-51 "Method for Determination of Trace Elements in Cement and Cement Raw Materials." Alternatively, for simplicity, the clinker 5 was crushed into fine powder, and the mixture was shaken for 1 minute with a water ratio of 10. The hexavalent chromium concentration was measured using a Pack Test (registered trademark) model KR-Cr manufactured by Kyoritsu Chemical Research Institute. 6+ It can also be measured and determined by

[0064] However, since the calorific value per unit of energy of the clinker 5 does not change significantly, when the amount of heat input from the second burner 20 is increased, it becomes necessary to decrease the amount of heat input from the first burner 10. If the amount of heat input from the first burner 10 is changed significantly, the thermal history of the clinker 5 may change significantly, which may affect its quality. Furthermore, when the clinker 5 is exposed to a reducing atmosphere, the mineral composition may change, which may affect its quality. From this perspective, the amount of heat input from the second burner 20 is preferably less than 50%, and more preferably less than 30%, of the amount of heat input from the first burner 10. The amount of heat input from the second burner 20 may be adjusted depending on the degree of deviation between the quantification result and the reference value. Various methods can be used to adjust the amount of heat input from the second burner 20. Examples of methods include changing the installation location of the second burner 20 in the Y and Z directions; tilting the insertion angle of the second burner 20 vertically from horizontal; changing the position of the tip 20a (see Figure 6) of the second burner 20 in the X direction; changing the wind speed blown from the second burner 20; and changing the type and particle size (ease of combustion) of the combustible waste RF1.

[0065] Fig. 6 is a diagram showing a portion extracted from Fig. 1. As shown in Fig. 6, the second burner 20 is preferably installed so that its tip 20a is located on the -X side of the center position x4c of the kiln hood 4 in the X direction. If the tip 20a of the second burner 20 protrudes toward the rotary kiln 2 from the center position x4c of the kiln hood 4, it is likely to block the flow of secondary air A2, which may reduce the combustion efficiency of the clinker 5. In addition, the increased surface area exposed to the high-temperature secondary air A2 may cause severe thermal damage to the second burner 20. [Example]

[0066] A simulation was carried out to examine the effect of changing the position of the second burner 20 on the rate at which the combustible waste RF1 blown in from the second burner 20 lands in the clinker 5. The simulation conditions are described below.

[0067] 7A to 7C are schematic diagrams illustrating the dimensions and shapes of the rotary kiln 2, kiln hood 4, and first burner 10 used in the simulation. Like FIG. 1, FIG. 7A is a schematic cross-sectional view of the rotary kiln 2 and kiln hood 4 taken along the XZ plane. FIG. 7B is a cross-sectional view taken along line BB in FIG. 7A, and FIG. 7C is a cross-sectional view taken along line CC in FIG. 7A.

[0068] The dimensions of each member used in the simulation will be described with reference to FIGS. 7A to 7C.

[0069] The length L2 of the rotary kiln 2 in the longitudinal direction (X direction) shown in FIG. 7A was set to 30,000 mm. The rotary kiln 2 shown in Figure 7A was tilted so that it moved 40 mm in the +Z direction as it moved 1,000 mm in the +X direction. That is, the tilt angle θ of the rotary kiln 2 shown in Figure 7A was set to θ = arctan(0.04) = 2.29°. The length L4 of the kiln hood 4 in the X direction shown in FIG. 7A was set to 3,500 mm. 7A, the tip 10a of the first burner 10 was positioned protruding 100 mm on the +X side (upstream side) from the clinker outlet 6. The clinker outlet 6 corresponds to an imaginary boundary surface parallel to the vertical direction that connects the rotary kiln 2 and the kiln hood 4.

[0070] The radius r2 (=½ of the inner diameter) of the inner space of the rotary kiln 2 shown in FIG. 7B was set to 2,350 mm. The radius r4 (half the outer diameter) of the outer wall portion of the kiln hood 4 shown in FIG. 7B was set to 3,100 mm.

[0071] The dimensions of each part of the kiln hood 4 shown in FIG. 7B were as follows: W41=4,700mm W42 = 6,200mm ·h41=2,600mm ·h42=3,550mm

[0072] As shown in FIG. 7C, the rotary kiln 2 had a rotation direction dr2 that was clockwise when viewed from the downstream side to the upstream side (when viewed in the +X direction).

[0073] In Figure 7C, the location where clinker 5 is retained within the rotary kiln 2 is defined by a slope 2s. When viewed in the X direction, this slope 2s is the area enclosed by end points 2s1 and 2s2. End point 2s1 is a point rotated by an angle θ1 in the direction opposite to the rotation direction dr2 of the rotary kiln 2, based on a line connecting the axis 2c of the rotary kiln 2 vertically (the line indicating the Y coordinate y2). On the other hand, end point s2 on the opposite side is a point rotated by an angle θ2 in the same direction as the rotation direction dr2 of the rotary kiln 2, based on the same line indicating the Y coordinate y2. The respective angles θ1 and θ2 were set to θ1 = 18.2° and θ2 = 63.7°.

[0074] The deviation y23 shown in Fig. 7C was set to 744 mm. This deviation y23 corresponds to the amount of deviation in the Y direction between the Y coordinate y3 of the center 3c of the clinker cooler 3 and the Y coordinate y2 of the axial center 2c of the rotary kiln 2, as described above with reference to Fig. 2.

[0075] Fig. 8 is a diagram for explaining the position of the axial center 20c of the second burner 20, which was verified by simulation. As shown in Fig. 8, three Y coordinates, H1, H2, and H3, and four Z coordinates, V1, V2, V3, and V4, were assumed as candidates for the position of the axial center 20c of the second burner 20. However, the position (Y, Z) = (H2, V2) was determined to be the position of the axial center 10c of the first burner 10.

[0076] Hereinafter, when describing the position of the axial center 20c of the second burner 20 on the YZ plane, the notation Hi-Vj (i = 1, 2, 3, j = 1, 2, 3, 4) is used. Using this notation, in this simulation, eleven locations were assumed as the position of the axial center 20c of the second burner 20: H1-V1, H1-V2, H1-V3, H1-V4, H2-V1, H2-V3, H2-V4, H3-V1, H3-V2, H3-V3, and H3-V4. Of these locations, six locations: H2-V3, H2-V4, H3-V1, H3-V2, H3-V3, and H3-V4, are located within the hatched area PA described above with reference to FIG. 4 and correspond to the embodiment.

[0077] H1, H2, and H3 were each spaced 1,000 mm apart, and V1, V2, V3, and V4 were each spaced 1,000 mm apart.

[0078] Waste plastics (waste plastics) were used as the combustible waste RF1 to be blown in from the second burner 20. Figure 9 is a graph showing the particle size distribution of the combustible waste RF1 assumed in this simulation. This particle size distribution is based on the measurement results of the particle size distribution of waste plastics sampled from a cement factory. The density of this waste plastic is 1.22 g / cm 3 It was said that.

[0079] The amount of waste plastic (combustible waste RF1) fed from the second burner 20 was set to 3 t / h. The secondary air A2 flowing into the rotary kiln 2 from the clinker cooler 3 side had a flow rate of 83,000 N m 3 / h and the temperature was set to 830°C.

[0080] During actual operation of the rotary kiln 2, the amount of air (primary air amount) blown into the rotary kiln 2 from the first burner 10 is approximately 10% to 14% of the flow rate of the secondary air A2. For this reason, it is assumed that the secondary air A2 is the dominant factor determining the behavior of the combustible waste RF1 blown into the rotary kiln 2 from the second burner 20, and that the primary air blown in from the first burner 10 has almost no effect. Under these circumstances, and from the perspective of reducing the amount of calculation, the amount of air blown in from the first burner 10 was set to zero.

[0081] Under the above-mentioned simulation conditions, the trajectory of the waste plastic blown from the second burner 20 and the position where it falls within the rotary kiln 2 were determined by simulation when the axis 20c of the second burner 20 was positioned at the 11 locations. The simulation was performed using FLUENT ver. 2019R3 software manufactured by ANSYS. Note that the diameter of the second burner 20 was set to zero in the calculation. In other words, the calculation was performed assuming that the waste plastic was blown in from the axis 20c as a point.

[0082] In order to verify the effect that differences in the wind speed of the waste plastic flow blown in from the second burner 20 have on the falling position of the waste plastic, simulations were conducted under two conditions: a wind speed of 20 m / s and a wind speed of 80 m / s.

[0083] In addition, in order to verify the effect that the X-direction position of the tip 20a of the second burner 20 (see Figure 6), in other words, the distance between the position where the waste plastic begins to be blown in and the rotary kiln 2 (clinker outlet 6), has on the position where the waste plastic falls, simulations were performed under two conditions: when the tip 20a of the second burner 20 is located at the downstream end face 4a of the kiln hood 4 (see Figure 6), and when it is located at the central point x4c (see Figure 6) in the X-direction of the kiln hood 4.

[0084] Fig. 10 is a diagram showing an example of a simulation result. Specifically, Fig. 10 shows the trajectory of the waste plastic when the position of the tip 20a of the second burner 20 in the X direction is the position of the downstream end face 4a of the kiln hood 4, the position of the axis 20c of the second burner 20 on the YZ plane is the position corresponding to H3-V3, and the wind speed of the waste plastic is 20 m / s.

[0085] As described above, in this simulation, no air flow (flame flow) is blown in from the first burner 10. Therefore, the waste plastic (combustible waste RF1) blown into the rotary kiln 2 from the second burner 20 moves along with the airflow of the secondary air A2 blown in from below, and all of it falls onto the inner wall surface (typically the bottom surface) of the rotary kiln 2. However, changing the position of the second burner 20 may affect the position at which the waste plastic falls onto the inner wall surface of the rotary kiln 2.

[0086] Figure 11 is a graph that analyzes the falling position of the fallen waste plastic based on the results of Figure 10, with the horizontal axis representing the distance from the clinker outlet 6 to the falling position and the vertical axis representing the amount of fallen waste plastic. According to this graph, it was confirmed through simulation that 80% of the input waste plastic fell to the bottom of the rotary kiln 2 between the clinker outlet 6 and the area 6.2 m from the clinker outlet 6 in the X direction.

[0087] When the amount of waste plastic that falls from the clinker outlet 6 in the +X direction (upstream) is added up, the longer the distance from the clinker outlet 6 to the point where this total amount reaches 80%, the longer the time the blown-in waste plastic will float inside the rotary kiln 2. In other words, the longer the distance from the clinker outlet 6 where the amount of falling waste plastic is 80% or more, the more likely it is that when a flame is actually blown from the first burner 10, the waste plastic will be completely burned by the flame before it falls.

[0088] From the above viewpoint, the position of the second burner 20 was changed, and the distance from the clinker outlet 6 to the point where the total amount of falling waste plastic reached 80% of the input amount was measured. The results are shown in Table 1.

[0089] [Table 1]

[0090] According to Table 1, when comparing the waste plastic air speeds of 20 m / s and 80 m / s with the tip 20a of the second burner 20 positioned at the downstream end surface 4a of the kiln hood 4, it was confirmed that there was no significant difference in the overall trend. This result suggests that the flow of secondary air A2 is dominant within the rotary kiln 2, and that the speed of the waste plastic flow from the second burner 20 has little effect on the location where the waste plastic falls.

[0091] Regarding the position of the axis 20c of the second burner 20 on the YZ plane, it can be seen that the drop position of the waste plastics tends to be farthest from the clinker outlet 6 when the Y coordinate is H1, and the drop position tends to get closer to the clinker outlet 6 in the order of H2 and H3. This is in line with the content described above with reference to FIG. 5. That is, the locations where the Y coordinate is H3 (H3-V1, H3-V2, H3-V3, H3-V4) are all located within the hatched area PA shown in FIG. 8 (FIG. 5), and this area corresponds to the area where the airflow of the secondary air A2 exhibits a downward airflow. Therefore, when combustible waste RF1 is blown into the rotary kiln 2 from the second burner 20 whose axis 20c is located at each of H3-V1, H3-V2, H3-V3, and H3-V4, it is difficult for the waste waste RF1 to float within the rotary kiln 2. Rather, it is likely to ride the downward airflow and fall toward the bottom of the rotary kiln 2 in a relatively short time. As a result, the probability that the combustible waste RF1 will fall toward the bottom of the rotary kiln 2 before being completely burned increases.

[0092] Regarding the position of the axis 20c of the second burner 20 on the YZ plane, it can be seen that among the four locations H3-V1, H3-V2, H3-V3, and H3-V4, where the combustible waste RF1 is blown into a relatively low location in the Z direction, the location H3-V3 or H3-V4 tends to have the waste plastic falling position closer to the clinker outlet 6.

[0093] When the position of the axis 20c is H2-V3 or H2-V4, there is a flow of secondary air A2 directed vertically downward as shown in Figure 5, and since the combustible waste RF1 is blown into a relatively low position in the Z direction, it is thought that the combustible waste RF1 is likely to fall toward the bottom of the rotary kiln 2 in a relatively short time.

[0094] Furthermore, according to Table 1, when the waste plastic wind speed is set to 20 m / s and the position of the tip 20a of the second burner 20 is at the downstream end face 4a of the kiln hood 4, and when the position of the tip 20a of the second burner 20 is at the center point x4c of the kiln hood 4, it can be seen that in the former case the waste plastic falling position tends to be closer to the clinker outlet 6. When the position of the axis 20c is H3-V1 or H3-V2, the distance from the clinker outlet 6 is relatively short under the former condition, whereas under the latter condition the distance from the clinker outlet 6 is greater than in the former case.

[0095] The reason for this is thought to be that by positioning the tip 20a of the second burner 20 at the central point x4c of the kiln hood 4, the position where the waste plastic starts to be blown in is closer to the clinker outlet 6, making it less likely to be caught in the airflow of the secondary air A2 and more likely to proceed in the X direction. On the other hand, even if the tip 20a of the second burner 20 is positioned at the central point x4c of the kiln hood 4, if the position of the axis 20c is H3-V3 or H3-V4, the combustible waste RF1 is blown into a relatively low position in the Z direction, and therefore is likely to fall toward the bottom of the rotary kiln 2 in a relatively short time. [Explanation of symbols]

[0096] 1: Cement manufacturing facility 2: Rotary kiln 2a: Inner wall of rotary kiln 2c: Rotary kiln shaft center 3: Clinker cooler 3c: Center of the clinker cooler 4: Kilnhood 4a: Downstream end of kiln hood 5: Clinker 6: Clinker outlet 10: First burner 10a: Tip of first burner 10c: Axis of the first burner 20: Second burner 20a: Tip of second burner 20c: Axis of the second burner A1: Atmosphere A2: Secondary air C1: Main fuel (pulverized coal) RF1: Combustible waste dr2: Rotation direction of clinker cooler

Claims

1. A method for operating a combustible waste injection device, comprising: The combustible waste blowing device comprises:

1. A combustible waste injection device attachable to a rotary kiln for manufacturing cement, the rotary kiln including a first burner into which a primary fuel is injected, the device comprising: a second burner that is different from the first burner and that blows combustible waste into the combustion chamber; When viewed in the blowing direction of the first burner, the second burner is arranged so that its axis is located within a region sandwiched between a first position vertically below the axis of the first burner and a second position 170° forward from the first position in a direction opposite to the rotation direction of the rotary kiln, with the axis as a reference; The second burner blows the combustible waste at a wind speed of 20 m / s to 80 m / s toward an internal space of the rotary kiln where a downward air current is generated within the rotary kiln, A method for operating a combustible waste injection device, comprising: monitoring a detection value of hexavalent chromium contained in cement clinker extracted from a clinker cooler connected to the rotary kiln; and, when the detection value exceeds a predetermined value, performing control to increase the amount of combustible waste injected from the second burner.

2. 2. A method for operating a combustible waste injection device as described in claim 1, characterized in that the second burner is arranged so that, when viewed in the blowing direction of the first burner, the axis of the second burner is located vertically below a horizontal plane passing through the axis of the first burner.

3. The first burner and the second burner are fixedly attached to a downstream end surface of a kiln hood connected to the downstream side of the rotary kiln, 3. A method for operating a combustible waste injection device as described in claim 1 or 2, characterized in that, when viewed from a direction parallel to the horizontal plane and perpendicular to the injection direction of the first burner, the position of the tip of the second burner is closer to the downstream end face of the kiln hood than the midpoint between an imaginary boundary plane parallel to the vertical direction connecting the rotary kiln and the kiln hood and the downstream end face of the kiln hood.

4. The method for operating a combustible waste injection device according to any one of claims 1 to 3, characterized in that the second burner injects the combustible waste into the rotary kiln with a calorific value less than the calorific value input from the first burner.

5. 5. The method for operating a combustible waste injection device according to claim 1, wherein the combustible waste injected from the second burner is general waste or industrial waste that is combustible and whose main component is one or more organic materials belonging to the group consisting of waste plastics, wood chips, ASR, waste tires, meat and bone meal, and biomass.

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