Cement clinker manufacturing method

Abstract

To efficiently reduce NOx in exhaust gases from cement manufacturing facilities. [Solution] A cement manufacturing facility comprising a raw material mill for crushing cement raw materials, a preheater for preheating the cement raw materials crushed in the raw material mill, a rotary kiln for heating the cement raw materials, a riser duct connecting the preheater and the rotary kiln, a dust collector installed downstream of the raw material mill, and an exhaust gas outlet for releasing exhaust gas that has passed through the dust collector, wherein a method for producing cement clinker by heating cement raw materials in a rotary kiln is provided, comprising a denitrification material supply device for supplying denitrification material to the riser duct, and a detector for detecting NOx and O2 concentrations in the exhaust gas from the preheater before the raw material mill, predicting the NOx value at the exhaust gas outlet converted to O2 10% from the NOx and O2 concentration detected by the detector, and controlling the amount of denitrification material supplied to the riser duct according to the predicted value.

Description

Technical Field

[0001] The present invention relates to a method for producing cement clinker in a cement manufacturing facility, which produces cement clinker while removing NOx contained in the exhaust gas from a rotary kiln.

Background Art

[0002] In a cement manufacturing facility, cement raw materials are fired in a firing furnace having a rotary kiln to produce cement clinker. At this time, by burning a heat energy raw material containing carbon with a burner, in addition to NOx originating from the heat energy raw material, nitrogen is oxidized at high temperature to generate thermal NOx. In order to reduce NOx in this exhaust gas, for example, the techniques described in the following patent documents are disclosed.

[0003] Patent Document 1 describes that a variable throttle device is provided in the riser flue connecting the kiln bottom of a kiln with a suspension preheater and a mixing chamber, and the flow rate of the kiln exhaust gas is controlled by adjusting the throttle amount of the throttle valve of the variable throttle device. At the same time, a denitration additive (such as ammonia) is ejected from a nozzle opening at the tip surface of the throttle valve and mixed with the kiln exhaust gas. It is also described that the throttle amount of the variable throttle device and the supply amount of the denitration additive are adjusted based on the detected value of NOx in the exhaust gas at the outlet of the cyclone at the uppermost stage.

[0004] Patent Document 2 describes that a denitration chemical is blown into the exhaust gas from which the cement raw material in the preheating device has been separated for denitration. In this case, the concentration of nitrogen oxides in the exhaust gas discharged from the exhaust gas outlet of the preheating device through which the exhaust gas into which the denitration chemical has been blown passes, the exhaust gas outlet of the raw material mill provided in the cement plant, or the exhaust chimney of the cement plant is detected, and the blowing flow rate of the denitration chemical is controlled based on the detected nitrogen oxide concentration.

[0005] Patent Document 3 describes a method for producing cement clinker while reducing carbon dioxide emissions by introducing a thermal energy raw material containing ammonia gas from a first inlet provided in a calcination furnace and burning the ammonia gas in the calcination furnace. [Prior art documents] [Patent Documents]

[0006] [Patent Document 1] Japanese Patent Application Publication No. 8-215537 [Patent Document 2] Japanese Patent Publication No. 2014-124599 [Patent Document 3] Japanese Patent Publication No. 2023-028050 [Overview of the project] [Problems that the invention aims to solve]

[0007] By the way, if NOx in the exhaust gas from the chimney of a cement manufacturing facility is managed and denitrification is performed by adding a denitrification agent to the preheater when it exceeds the standard value, there is a very large time lag. On the other hand, if NOx is managed at the exhaust gas outlet of a preheating device, it is difficult to manage accurately because it differs from the NOx value at the exhaust gas outlet of the entire cement manufacturing facility. In either case, if there are large fluctuations in NOx or O2, the amount of denitrification agent introduced may be too much or too little.

[0008] This invention has been made in view of these circumstances, and aims to efficiently reduce NOx in exhaust gas from cement manufacturing facilities. [Means for solving the problem]

[0009] The present invention relates to a cement clinker manufacturing method, comprising a cement manufacturing facility comprising: a raw material mill for crushing cement raw materials; a preheater for preheating the cement raw materials crushed in the raw material mill; a rotary kiln for heating the cement raw materials; a riser duct connecting the preheater and the rotary kiln; a dust collector installed downstream of the raw material mill; and an exhaust gas outlet for releasing exhaust gas that has passed through the dust collector, wherein cement clinker is manufactured by heating the cement raw materials in the rotary kiln, The system includes a denitrification material supply device that supplies denitrification material to the riser duct, and a detector that detects NOx and O2 concentrations in the exhaust gas from the preheater before reaching the raw material mill. The system predicts the NOx value at the exhaust gas outlet, converted to 10% O2, from the NOx and O2 concentration values ​​detected by the detector, and controls the amount of denitrification material supplied to the riser duct according to the predicted value.

[0010] By detecting the NOx and O2 concentrations in the exhaust gas from the preheater before reaching the raw material mill and controlling the amount of denitrification material supplied to the riser duct, it is possible to respond quickly to changes in the concentration in the exhaust gas. Furthermore, by predicting the NOx value at the exhaust gas outlet of the cement manufacturing facility in terms of O2 10% from the exhaust gas before reaching the raw material mill and controlling the amount of denitrification material supplied according to this predicted value, it is possible to reliably reduce NOx in the exhaust gas from the entire cement manufacturing facility.

[0011] The NOx value converted to O2 10% is the NOx value when the O2 concentration is assumed to be 10%, and it assumes the NOx value at the exhaust gas outlet. The O2 concentration in the exhaust gas just before it enters the raw material mill is lower than 10% (for example, 3%), so the NOx value converted to O2 10% at the exhaust gas outlet is predicted from the detected value, and the amount of denitrification material supplied is controlled accordingly. This makes it possible to control the NOx at the exhaust gas outlet within an appropriate range. Moreover, since the exhaust gas is detected just before it enters the raw material mill, the denitrification material can be supplied without a time lag, and the NOx in the exhaust gas can be efficiently reduced. Furthermore, the denitrification material is supplied to the rising duct of the rotary kiln, and because this is a part close to the kiln's tail end, the temperature is high, resulting in good reaction efficiency (denitrification efficiency) of the denitrification material.

[0012] In the cement clinker manufacturing method of the present invention, a calcination furnace is connected to the rotary kiln, and gas ventilated from the denitrification material supply device is supplied to the calcination furnace. The ventilation from the denitrification material supply device contains volatile gases from the denitrification material, and by supplying these to the calcination furnace, the gases with denitrification effects can be effectively utilized.

[0013] Furthermore, the system may have a sludge storage tank for storing sludge that will be used as a raw material for cement, and may supply gas ventilated from the sludge storage tank to the calcination furnace. In the case of sludge storage tanks, the ventilation system contains ammonia gas, so by supplying this gas to a calcination furnace, it is possible to effectively utilize the gas, which has a denitrification effect.

[0014] In the cement clinker manufacturing method of the present invention, it is preferable that two or more rotary kilns, each having a preheater and a riser duct, are provided, and that the denitrification material supply device is connected to the riser duct of each rotary kiln.

[0015] By detecting the NOx and O2 concentrations in the exhaust gas from each preheater and supplying denitrification material to the corresponding rotary kiln riser duct, the system can respond quickly and efficiently suppress the release of NOx into the atmosphere, even when multiple rotary kilns are installed. [Effects of the Invention]

[0016] According to the present invention, since the NOx concentration and O2 concentration in the exhaust gas from the preheater are detected and the denitration material is supplied, it is possible to promptly respond to fluctuations in the NOx concentration, and since the denitration material is supplied to the riser duct of the rotary kiln, the denitration efficiency is also good. In this case, since the concentration at the outlet is predicted and controlled, the NOx in the exhaust gas discharged into the atmosphere can be efficiently reduced.

Brief Description of the Drawings

[0017] [Figure 1] It is a schematic diagram showing a cement manufacturing facility according to an embodiment of the present invention. [Figure 2] It is a schematic diagram of a main part showing an example when a plurality of rotary kilns are provided in a cement manufacturing facility.

Embodiments for Carrying Out the Invention

[0018] Hereinafter, embodiments of the present invention will be described with reference to the drawings.

[0019] FIG. 1 shows an embodiment of a cement manufacturing facility. This cement manufacturing facility 1 includes a raw material storage 2 for storing limestone, clay, silica, iron raw materials, etc. as cement raw materials individually, a raw material mill and dryer 3 for pulverizing and drying these cement raw materials, a preheater 4 for preheating the powdery cement raw materials obtained by this raw material mill, a cement kiln 5 for firing the cement raw materials preheated by the preheater 4, a clinker cooler 6 for cooling the cement clinker after firing in the cement kiln 5, and the like.

[0020] The cement kiln 5 is a horizontally oriented cylindrical rotary kiln that is slightly inclined downward from the kiln tail part 5a toward the kiln front part 5b and rotates around its axis. Then, the cement raw materials in the raw material storage bin 2 are crushed and dried by the raw material mill and the dryer 3, sent to the preheater 4, preheated, and then supplied to the kiln bottom part 5a of the cement kiln 5. In the cement kiln 5, while the cement raw materials supplied to the kiln bottom part 5a are sent to the kiln front part 5b, they are heated and fired to about 1450 °C by the burner 7 in the kiln front part 5b during the sending process to produce cement clinker, and this cement clinker is sent out from the kiln front part 5b to the clinker cooler 6. The cement clinker is cooled to a predetermined temperature in the clinker cooler 6 and then sent to the finishing process. Note that reference numeral 9 in Fig. 1 indicates a calciner connected to the rotary kiln 5 together with the preheater 4, and the cement raw materials preheated by the preheater 4 are calcined by the burner 10. In addition, in this cement manufacturing facility 1, in addition to limestone and the like, sludge such as sewage sludge is also used as the cement raw material, and reference numeral 11 indicates a sludge supply device. In this sludge supply device 11, the sludge stored in the sludge storage tank 12 is supplied by the pump 13 through the sludge supply pipe 14 to the kiln bottom part 5a, drying equipment (not shown), etc.

[0021] On the other hand, the exhaust gas generated in the cement kiln 5 is sent to the preheater 4 through the rising duct 15 in the kiln bottom part 5a of the cement kiln 5, and is attracted by the induced draft fan 16 arranged between the preheater 4, the raw material mill, and the dryer 3. As a result, after flowing through the preheater 4 from the bottom to the top in the opposite direction to the cement raw materials, it is introduced into the raw material mill and the dryer 3. The raw material mill and the dryer 3 are configured to simultaneously grind and dry the cement raw materials when the exhaust gas from the cement kiln 5 is introduced. The exhaust gas from the raw material mill and the dryer 3 is discharged into the atmosphere from the chimney (the exhaust gas outlet of the present invention) 18 as shown by the arrow in Fig. 1 via the electrostatic precipitator 17.

[0022] Detectors 21 to 23 for detecting the NOx concentration and the O2 concentration are provided on the rising duct 15, the downstream side of the induced draft fan 16, and the upstream side of the chimney 18, respectively. They are the first detector 21, the second detector 22, and the third detector 23 from the upstream side. These detectors 21-23 measure the concentrations of nitric oxide (NO) and nitrogen dioxide (NO2) present in the exhaust gas as NOx, based on methods such as chemiluminescence and spectrophotometric analysis. They can also detect O2 concentration along with NOx concentration.

[0023] Furthermore, a denitrification material supply device 25 is connected to the riser duct 15, and based on the detection results of detectors 21 to 23, the denitrification material is supplied to the riser duct 15. A denitrification material supply pipe 28 is connected to this denitrification material supply device 25 between the denitrification material storage tank 26 and the riser duct 15, and this denitrification material supply pipe is equipped with a pump inlet valve 29, a pump 30, a flow meter 31, and an inlet shut-off valve 32. As a denitrification method, a catalyst-free reduction method using ammonia water as the denitrification agent is employed. By adding ammonia (NH3) to the exhaust gas, nitric oxide (NO) and nitrogen dioxide (NO2) as NOx are reduced to nitrogen (N2) and water vapor (H2O) without the use of a catalyst (gas-phase catalyst-free). The maximum denitrification rate is obtained when the exhaust gas temperature is in the range of 900°C to 1000°C.

[0024] In Figure 1, reference numeral 35 indicates a control device for controlling the supply amount of denitrification material. Based on the NOx concentration detected by detectors 21-23, it calculates the supply amount of denitrification material and drives the pump 30 to supply the required amount of denitrification material to the riser duct 15. This control device 35 is composed of a computer equipped with a processing unit, memory, etc.

[0025] Furthermore, in the sludge storage tank 12 of the sludge supply device 11 and the denitrification material storage tank 26 of the denitrification material supply device 25, ammonia gas volatilizes from the denitrification material and sludge, so the inside of the tanks 12 and 26 is ventilated by sucking out this ammonia gas with pumps 36 and 37. This ammonia gas is sent by pumps 36 and 37 to the thermal energy raw material supply system 19 of the calcination furnace 9 of the kiln 5, and supplied to the calcination furnace 9 together with the thermal energy raw material.

[0026] In the cement manufacturing facility 1 configured in this way, the exhaust gas generated in the rotary kiln 5 is drawn in by the induced fan 16, introduced to the raw material mill and dryer 3 via the preheater 4, and then released into the atmosphere through the chimney 18 after passing through the electrostatic precipitator 17. Along the way, NOx and O2 concentrations in the exhaust gas are detected by detectors 21-23 at the riser duct 15, the downstream side of the induced draft fan 16, and the upstream side of the chimney 18, respectively. Of these detectors 21 to 23, the denitrification material is supplied to the riser duct 15 by the denitrification material supply device 25 connected to the riser duct 15, based on the detection results of the second detector 22, which is mainly located downstream of the induced fan 16 (upstream of the raw material mill and dryer 3).

[0027] The specific control standards used for the addition of this denitrification agent are set as follows: The standard value for the NOx concentration in the exhaust gas released from the chimney 18 is set to 460 ppm or less, calculated as an O2 10% equivalent concentration. Downstream of the induced fan 16 where the second detector 22 is installed, the O2 3% equivalent concentration is set to 460 × (21-2) ÷ (21-10) = 795 ppm. Therefore, the upper control value for the NOx value to be managed by the second detector 22 is set to 750 ppm, and the lower control value is set to 700 ppm. These upper and lower control values ​​are NOx values ​​used to manage the NOx concentration detected by the second detector 22 so that it remains within these control ranges, and are stored in the memory of the control device 35.

[0028] In this case, the detected values ​​will fluctuate to some extent, so for example, the average value of the detected values ​​over a 4-minute period is calculated and compared with the control value. If the average value exceeds the upper control value, the pump inlet valve 29 and the shut-off valve 32 are opened, and the pump 30 is driven to start control (start of denitrification material supply). The control device 35 sequentially receives the detected values ​​sent from the detector 22 at predetermined intervals. For example, it checks the fluctuation range between the input value and the previous input value. If the fluctuation range is within a predetermined range, it considers that the input value is continuing, and if it continues for 4 minutes, it instructs the denitrification material supply device 25 to supply the denitrification material. In this case, the amount of denitrification material supplied is set according to the difference between the detected NOx concentration and the upper control value (750 ppm). The amount of denitrification material supplied from the denitrification material supply pipe 28 is checked by the flow meter 31, and the pump inlet valve 29 and the shut-off valve 32 are controlled as needed. When the average value falls below the lower control value, the pump 30 is stopped and control is terminated.

[0029] In addition to these control values, an upper limit of 850 ppm and a lower limit of 680 ppm are set. Of these, the upper limit is determined by the NOx concentration in O23% equivalent detected by detector 22. If the detected value exceeds the upper limit, control is initiated (denitrification material is added) without waiting 4 minutes. On the other hand, regarding the lower limit, if the detected value falls below the lower control value without waiting 4 minutes, the pump 30 is stopped and the supply of denitrification material is halted, for example, if the value falls below the lower limit by 30 seconds. In all control cases, as mentioned above, the amount of denitrification agent added is determined by the difference between the upper control value (750 ppm) and the detected value.

[0030] As described above, the second detector 22 detects the NOx and O2 concentrations in the exhaust gas from the induced fan 16. Therefore, control can be performed based on the detected NOx and O2 concentrations in the exhaust gas from the rotary kiln 5 at a relatively early stage. Furthermore, since the control is performed by predicting the NOx concentration in the exhaust gas from the chimney 18, the NOx concentration in the exhaust gas can be reliably reduced.

[0031] Furthermore, the third detector 23, located at the inlet of the chimney 18, can directly detect the NOx and O2 concentrations in the exhaust gas actually released from the chimney 18, and the detection results are fed back to the control device 35. The values ​​detected by this third detector 23 are the O2 10% equivalent concentrations mentioned above, and the control device 35 fine-tunes the control values ​​based on the detection results from the third detector 23.

[0032] On the other hand, the first detector 21, which is installed in the rising duct 15, sends its detected values ​​to the control device 35 in the same way as the other detectors 22 and 23. However, since the detected values ​​are from an environment with a lot of dust, the absolute value of the detected value itself is not used. Instead, only the trend is grasped from the fluctuations in the detected value, and it is used to monitor the fluctuations of NOx and O2 in the exhaust gas and to confirm whether the detection result from the second detector 22 is a detected value that largely reflects those fluctuations.

[0033] Figure 2 is a schematic representation of a cement manufacturing facility with multiple rotary kilns installed. Figure 2 shows five rotary kilns 5A to 5E and two calcination furnaces 9A and 9B. Each rotary kiln 5A to 5E has a riser duct 15A to 15E connected to its tail section 5a. Although not shown, a preheater and an induced draft fan are also connected, and the exhaust gas from the preheater is sent downstream by the induced draft fan (see Figure 1). Furthermore, as a denitrification material supply device 40, multiple denitrification material supply pipes 28A to 28E are connected to a denitrification material storage tank 26 for storing the denitrification material, and each of these is connected to the riser ducts 15A to 15E of the rotary kilns 5A to 5E. Furthermore, each denitrification material supply pipe 28A to 28E is equipped with a pump inlet valve 29A to 29E, a pump 30A to 30E, a flow meter 31A to 31E, and an inlet shut-off valve 32A to 32E, respectively.

[0034] On the other hand, sludge volatile gas is supplied to the calcination furnaces 9A and 9B by pumps 46 and 47 from a sludge ventilation pipe 45 connected to a sludge storage tank (not shown in Figure 2) where sludge is stored. In addition, a denitrification material ventilation pipe 48 is connected from the denitrification material storage tank 26 of the denitrification material supply device 40, so that the denitrification material volatile gas from the denitrification material storage tank 26 can also be supplied to the calcination furnaces 9A and 9B. If there is no calcination furnace, it may be supplied to the burner 7. Note that these calcination furnaces 9A and 9B are installed to correspond to two of the five rotary kilns 5A to 5E, but one or more is sufficient.

[0035] The exhaust gases from the five rotary kilns 5A to 5E are drawn in by induced draft fans located downstream of each preheater and introduced into the raw material mill, dryer, and raw material storage facility. They are then discharged into the atmosphere through chimneys via electrostatic precipitators (see Figure 1). In this case, although multiple chimneys are provided, the exhaust gas flow path is combined into multiple paths along the way and discharged through multiple chimneys. Therefore, the number of chimneys is not necessarily the same as the number of rotary kilns 5A to 5E.

[0036] Furthermore, detectors are provided in the riser ducts 15A to 15E, downstream of the induced draft fan, and upstream of the chimney. The detected values ​​from these detectors are collected in the control unit, which controls the denitrification material supply device 40. Figure 2 shows only the detectors 22A to 22E provided in each of the riser ducts 15A to 15E.

[0037] In the cement manufacturing facility configured in this way, the NOx and O2 concentrations in the exhaust gas are detected by detectors 22A to 22E in the riser ducts 15A to 15E. The detected values ​​are compared with a standard value set by the O2 10% equivalent concentration, and if necessary, the denitrification material is supplied to the riser ducts 15A to 15E of the rotary kilns 5A to 5E by the denitrification material supply device 40. In this case, since detectors 22A to 22E are provided for each riser duct 15A to 15E, the denitrification material is supplied to the riser duct corresponding to the detector that detected an abnormal value.

[0038] In this cement manufacturing facility, NOx in the exhaust gas from multiple rotary kilns 5A to 5E can be appropriately controlled, while reducing NOx in the exhaust gas of the entire cement manufacturing facility.

[0039] It should be noted that the present invention is not limited to the embodiments described above, and various modifications can be made without departing from the spirit of the invention. [Explanation of Symbols]

[0040] 1. Cement manufacturing equipment 2. Raw material storage 3. Raw material mill and dryer 4 Preheater 5, 5A~5E Rotary Kiln 9,9A,9B Tempering furnace 10 burners 11. Sludge supply device 12 Sludge storage tanks 13 pumps 14 Sludge supply pipe 15, 15A~15E Riser duct 16 Inducing Fan 17 Dust collector 18. Chimney (exhaust gas outlet) Detectors 21-23, 22A-22E 25,40 Denitrification material supply equipment 26 Denitrification material storage tank 29, 29A~29E Pump inlet valve 30, 30A~30E pumps 31,31A~1E Flow meter 32, 32A~32E Shut-off valves 28,28A~28E Denitrification material supply pipe 35 Control device 36,37 Pumps 45 Sludge ventilation pipe 48 Denitration material ventilation pipe

Claims

1. A cement manufacturing facility comprising a raw material mill for crushing cement raw materials, a preheater for preheating the cement raw materials crushed in the raw material mill, a rotary kiln for heating the cement raw materials, a riser duct connecting the preheater and the rotary kiln, a dust collector installed downstream of the raw material mill, and an exhaust gas outlet for releasing exhaust gas that has passed through the dust collector, wherein a method for producing cement clinker is provided, in which the cement raw materials are heated in the rotary kiln. A denitrification material supply device that supplies denitrification material to the aforementioned riser duct, and a device that measures the NOx concentration and Ox concentration in the exhaust gas from the preheater before the raw material mill. ２ A detector is provided to detect the concentration, and the NOx concentration and O are measured by the detector. ２ From the detected concentration, O at the exhaust gas outlet ２ A method for producing cement clinker, characterized by predicting the NOx value converted to 10% and controlling the amount of denitrification material supplied to the riser duct according to the predicted value.

2. The cement clinker manufacturing method according to claim 1, characterized in that a calcination furnace is connected to the rotary kiln, and gas ventilated from the denitrification material supply device is supplied to the calcination furnace.

3. The cement clinker manufacturing method according to claim 3, characterized in that it has a sludge storage tank for storing sludge that will be used as a raw material for cement, and that gas ventilated from the sludge storage tank is supplied to the calcination furnace.

4. The cement clinker manufacturing method according to claim 1, characterized in that two or more rotary kilns, each having a preheater and a riser duct, are provided, and the denitrification material supply device is connected to the riser duct of each rotary kiln.

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