Fluidized bed sludge incinerator and automatic combustion control method for fluidized bed sludge incinerator

Abstract

To decrease the N2O concentration in exhaust by controlling the fluidizing condition of a sand layer according to temperature differences measured by sand layer temperature measuring instruments disposed in various positions in the sand layer.SOLUTION: A fluidized bed type sludge incineration furnace comprising a sand layer and a freeboard section formed above the sand layer to combust sludge fed thereinto, is characterized by comprising a plurality of temperature measuring instruments disposed in the sand layer to measure a temperature at a plurality of positions in the sand layer, and a controller that calculates the difference of the highest temperature and the lowest temperature in the sand layer measured by the temperature measurement instruments, determines the amount of primary air to be fed into the sand layer according to the temperature difference value to control the amount of the primary air to be fed into the sand layer, and controls the primary combustion air so as to increase the amount of the primary air to be fed into the sand layer when the temperature difference exceeds a specified upper limit value, and to decrease the amount of the primary air to be fed into the sand layer when the temperature difference is below a specified lower limit value.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a fluidized bed sludge incinerator for burning sludge and an automatic combustion control method for a fluidized bed sludge incinerator. [Background technology]

[0002] Sewage treatment plants are equipped with sludge incinerators such as fluidized bed incinerators to burn sewage sludge. A fluidized bed incinerator is a multi-stage combustion incinerator equipped with a cylindrical incinerator body that has a sand layer (fluidized bed) that uses sand as a fluidizing medium and a freeboard section that serves as a combustion chamber, and processes the sludge through the processes of drying, gasification, and combustion.

[0003] Sewage sludge is rich in nitrogen, and its combustion exhaust gas contains N2O, which has a strong global warming effect. Therefore, it is desirable to minimize the amount of N2O emitted from incinerators. Furthermore, depending on the combustion conditions of the incinerator, the amount of harmful unburned matter such as carbon monoxide emitted from the chimney may increase, making it necessary to suppress the amount of carbon monoxide emitted.

[0004] Patent Document 1 describes a fluidized bed sludge incinerator that is equipped with an N2O concentration sensor that measures the N2O concentration of the combustion gas discharged from the incinerator body, and a control device that adjusts the amount of combustion air based on the measurement value of the N2O concentration sensor, and that limits the fluidization range of the sand layer based on the amount of combustion air.

[0005] Patent Document 2 describes a combustion control method for a fluidized bed sludge incinerator, in which a hearth thermometer that measures the hearth temperature is used as a fluidization state monitoring means, and if the measured value deviates from an appropriate range, it is determined that poor fluidization has occurred, and the amount of fluidizing air is increased to restore the fluidization state, and if the measured value returns to the appropriate range, the amount of fluidizing air is reduced again to continue stable operation. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] Japanese Patent Application Laid-Open No. 2016-142447 [Patent Document 2] Japanese Patent Application Publication No. 3-244912 Summary of the Invention [Problem to be solved by the invention]

[0007] Conventionally, a CO concentration meter is used for combustion control, but the method of Patent Document 1 requires an N2O concentration meter for combustion control. Patent Document 2 proposes a method of using a hearth thermometer to determine whether the fluidity state is good or bad based on the rate of change of the measured value, or a method of using multiple hearth thermometers to determine whether the fluidity state is good or bad based on the temperature difference between them. However, there is a problem in that if the overall hearth temperature fluctuates due to changes in the properties of the incineration material, it is not possible to detect a deterioration in the fluidity state. In fluidized bed sludge incinerators, the deterioration of the sand layer fluidity and the resulting unstable operation are major problems. This is because the primary air volume was reduced too much in an attempt to reduce the N2O concentration. The present invention aims to reduce the N2O concentration in exhaust gas by controlling the fluidization state of the sand layer based on the temperature difference measured by sand layer temperature measuring devices installed at various points in the sand layer. [Means for solving the problem]

[0008] As a result of intensive research by the inventors to solve the above problems, the applicant discovered that when multiple sand layer temperature measuring devices are installed in the sand layer, the above problems can be solved by setting upper and lower limit values ​​for the temperature difference between the highest and lowest sand layer temperatures indicated by these multiple sand layer temperature measuring devices, and controlling the amount of primary air supplied to the sand layer when the temperature difference exceeds the upper limit value and when the temperature difference falls below the lower limit value, thereby completing the present invention.

[0009] The embodiments of the present invention that solve the above problems are as follows. (1) A fluidized bed sludge incinerator that has a sand layer and a freeboard formed above the sand layer and burns sludge introduced into it, a plurality of temperature measuring devices provided in the sand layer portion for measuring the temperature of a plurality of locations in the sand layer; a control device that calculates the temperature difference between the maximum and minimum temperatures of the sand layer measured by the temperature measuring device, determines the amount of primary air to be supplied to the sand layer section based on the value of the temperature difference, and controls the amount of primary air to be supplied to the sand layer section, so that when the temperature difference exceeds a predetermined upper limit value, the amount of primary air to be supplied to the sand layer section is increased, and when the temperature difference falls below a predetermined lower limit value, the amount of primary air to be supplied to the sand layer section is decreased; A fluidized bed sludge incinerator comprising: (2) The fluidized bed sludge incinerator described in (1) above, characterized in that the control device is a control device that controls the amount of primary air supplied to the sand layer to increase by 1 to 5% when the temperature difference exceeds the predetermined upper limit value, and controls the amount of primary air supplied to the sand layer to decrease by 1 to 5% when the temperature difference falls below the predetermined lower limit value. (3) A fluidized bed sludge incinerator according to (2) above, characterized in that the predetermined upper limit is set to a value of 15°C or higher, and the predetermined lower limit is set to a value below 15°C. (4) A fluidized bed sludge incinerator having a sand layer and a freeboard formed above the sand layer, in which sludge is burned, a plurality of temperature measuring devices provided in the sand layer portion for measuring the temperature of a plurality of locations in the sand layer; a control device that calculates the temperature difference between the maximum and minimum temperatures of the sand layer measured by the temperature measuring device and the rate of change of said temperature difference, determines the amount of primary air to be supplied to said sand layer section based on the value of the rate of change of said temperature difference, and controls the amount of primary air to be supplied to said sand layer section, so that when the rate of change of said temperature difference exceeds a predetermined upper limit value, the amount of primary air to be supplied to said sand layer section is increased, and when the rate of change of said temperature difference falls below a predetermined lower limit value, the control device controls so that the amount of primary air to be supplied to said sand layer section is decreased; A fluidized bed sludge incinerator comprising: (5) A fluidized bed sludge incinerator according to (4) above, characterized in that the control device is a control device that controls the amount of primary air supplied to the sand layer to increase by 1 to 5% when the rate of change of the temperature difference exceeds the predetermined upper limit value, and controls the amount of primary air supplied to the sand layer to decrease by 1 to 5% when the rate of change of the temperature difference falls below the predetermined lower limit value. (6) A fluidized bed sludge incinerator according to (5) above, characterized in that the predetermined upper limit is set to a value of 15°C / h or more, and the predetermined lower limit is set to a value less than 15°C / h. (7) A CO concentration measuring device is provided to measure the CO concentration in the exhaust gas discharged from the furnace outlet of the incinerator body of the fluidized bed sludge incinerator, The fluidized bed sludge incinerator according to any one of (1) to (6) above, characterized in that the control device is a control device that controls so as to reduce the amount of primary air supplied to the sand layer when the CO concentration in the exhaust gas measured by the CO concentration measuring device exceeds a predetermined CO concentration upper limit value, and to increase the amount of primary air supplied to the sand layer when the CO concentration in the exhaust gas measured by the CO concentration measuring device falls below a predetermined CO concentration lower limit value. (8) The fluidized bed sludge incinerator according to (7) above, characterized in that the control device is a control device that controls so as to reduce the amount of primary air supplied to the sand layer by 1 to 5% when the CO concentration in the exhaust gas measured by the CO concentration measuring device exceeds a predetermined CO concentration upper limit value, and to increase the amount of primary air supplied to the sand layer by 1 to 5% when the CO concentration in the exhaust gas measured by the CO concentration measuring device falls below a predetermined CO concentration lower limit value. (9) The fluidized bed sludge incinerator according to (7) or (8) above, wherein the predetermined upper limit of the CO concentration is 10 to 20 PPM, and the predetermined lower limit of the CO concentration is 0 to 10 PPM. (10) An automatic combustion control method for a fluidized bed sludge incinerator that has a sand layer and a freeboard formed above the sand layer and burns introduced sludge, comprising: A method for automatic combustion control of a fluidized bed sludge incinerator, characterized in that a plurality of temperature measuring devices are provided in the sand layer section to measure the temperature of the sand layer at different positions, the temperature difference between the highest and lowest temperatures of the sand layer measured at the plurality of positions is calculated, and when the temperature difference exceeds a predetermined upper limit value, the amount of primary air supplied to the sand layer section is increased, and when the temperature difference falls below a predetermined lower limit value, the amount of primary air supplied to the sand layer section is decreased. (11) An automatic combustion control method for a fluidized bed sludge incinerator according to (10) above, characterized in that when the temperature difference exceeds the predetermined upper limit, the amount of primary air supplied to the sand layer is increased by 1 to 5%, and when the temperature difference falls below the predetermined lower limit, the amount of primary air supplied to the sand layer is decreased by 1 to 5%. (12) An automatic combustion control method for a fluidized bed sludge incinerator according to (11) above, characterized in that the predetermined upper limit is set to a value equal to or higher than 15°C, and the predetermined lower limit is set to a value less than 15°C. (13) An automatic combustion control method for a fluidized bed sludge incinerator that has a sand layer and a freeboard formed above the sand layer and burns introduced sludge, comprising: a temperature difference between the highest and lowest temperatures of the sand layer measured by the temperature measuring devices and the rate of change of said temperature difference; and if the rate of change of said temperature difference exceeds a predetermined upper limit, the amount of primary air supplied to said sand layer is increased; and if the rate of change of said temperature difference falls below a predetermined lower limit, the amount of primary air supplied to said sand layer is decreased. (14) An automatic combustion control method for a fluidized bed sludge incinerator according to (13) above, characterized in that when the rate of change of the temperature difference exceeds the predetermined upper limit, the amount of primary air supplied to the sand layer is increased by 1 to 5%, and when the rate of change of the temperature difference falls below the predetermined lower limit, the amount of primary air supplied to the sand layer is decreased by 1 to 5%. (15) An automatic combustion control method for a fluidized bed sludge incinerator according to (14) above, characterized in that the predetermined upper limit is set to a value equal to or greater than 15°C / h, and the predetermined lower limit is set to a value less than 15°C / h. (16) measuring the CO concentration in the exhaust gas discharged from the furnace outlet of the incinerator body of the fluidized bed sludge incinerator with a CO concentration meter; When the CO concentration in the exhaust gas measured by the CO concentration measuring device exceeds a predetermined CO concentration upper limit value, the amount of primary air supplied to the sand layer portion is reduced, The automatic combustion control method for a fluidized bed sludge incinerator according to any one of (10) to (15) above, characterized in that when the CO concentration in the exhaust gas measured by the CO concentration measuring device falls below a predetermined CO concentration lower limit value, the amount of primary air supplied to the sand layer section is increased. (17) When the CO concentration in the exhaust gas exceeds a predetermined CO concentration upper limit value, the amount of primary air supplied to the sand layer is reduced by 1 to 5%; The automatic combustion control method for a fluidized bed sludge incinerator according to (16) above, characterized in that when the CO concentration in the exhaust gas falls below a predetermined CO concentration lower limit, the amount of primary air supplied to the sand layer section is increased by 1 to 5%. (18) The automatic combustion control method for a fluidized bed sludge incinerator according to (16) or (17), wherein the predetermined CO concentration upper limit value is 10 to 20 PPM, and the predetermined CO concentration lower limit value is 0 to 10 PPM. [Effects of the Invention]

[0010] According to the present invention, the fluidization state of the sand layer can be controlled based on the temperature difference measured by sand layer temperature measuring devices installed at various points in the sand layer, thereby reducing the N2O concentration in the exhaust gas. [Brief explanation of the drawings]

[0011] [Figure 1] FIG. 1 is a schematic diagram of a fluidized bed sludge incinerator according to an embodiment of the present invention. [Figure 2]FIG. 2 is a diagram showing an example of the arrangement of sand layer temperature measuring devices for measuring the temperature of the sand layer in the incinerator body of the fluidized bed sludge incinerator according to an embodiment of the present invention. [Figure 3] FIG. 3 is a diagram showing the sand layer temperature difference, the sand layer temperature change rate, and the primary air flow control state in the embodiment of the present invention. [Figure 4] FIG. 4 is a diagram showing the relationship between the furnace outlet temperature and the N2O concentration in the exhaust gas discharged from the furnace outlet in an embodiment of the present invention. [Figure 5] FIG. 5 is a graph showing that there is a high correlation between the N2O concentration value at the chimney outlet and the CO concentration value at the ceramic filter outlet. DETAILED DESCRIPTION OF THE INVENTION

[0012] A fluidized bed sludge incinerator and an automatic combustion control method therefor according to an embodiment of the present invention will be described in detail below with reference to the drawings.

[0013] 1 is a schematic diagram of a fluidized bed sludge incinerator 1 according to one embodiment of the present invention. The fluidized bed sludge incinerator 1 is an incinerator that uses fluidized sand 17 as a heat medium to form a bubbling fluidized bed together with sludge M and combusts the fluidized bed. The incinerator body 3 of the fluidized bed sludge incinerator 1 has a sand layer section S (fluidized bed) located at the bottom and a freeboard section F located above the sand layer section S, and is equipped with a sludge inlet 6 formed in the side wall of the incinerator body 3, a furnace outlet 4 located at the top of the incinerator body 3, a primary air supply section 7 located at the bottom of the incinerator body 3 and supplying air for fluidization, a secondary air supply section 9 located above the primary air supply section 7 and supplying secondary air to the freeboard section F, multiple sand layer temperature measuring devices 10, multiple freeboard temperature measuring devices 11, and a control device 27 that controls the amount of primary air supplied to the primary air supply section 7 based on the measurement values ​​of the sand layer temperature measuring device 10 or the sand layer temperature measuring device 10 and the freeboard temperature measuring device 11.

[0014] 2A and 2B, the sand layer temperature measuring devices 10 are installed in two tiers, upper and lower, spaced apart in the vertical direction of the sand layer, with four devices installed in the lower tier, offset by 90 degrees in the circumferential direction as shown in Fig. 2A, and four devices installed in the upper tier, offset by 45 degrees in the circumferential direction from the installation position of the lower tier, as shown in Fig. 2B. In this embodiment, three freeboard temperature measuring devices 11 are installed directly above the sand layer, offset by 120 degrees in the circumferential direction, for example. The temperature is low near the walls of the incinerator body 3, and the temperature of the sand layer can be measured more than 150 to 200 mm from the inner wall, so it is preferable to position a thermocouple or other temperature measuring device to measure the temperature about 300 mm from the inner wall.

[0015] The fluidized bed sludge incinerator 1 has a sludge supplying device 5 that charges sludge M into the sand layer S, and the sludge M is charged from the sludge supplying device 5 into the sand layer S inside the incinerator body 3. The fluidized bed sludge incinerator 1 is equipped with a fluidized bed blower 21 that supplies combustion air, an air preheater 15 that preheats the combustion air, an air cooler 25 that receives preheated combustion air flowing out from the air preheater 15 and also receives outside air from a cooling blower 23, a total air volume control valve 31 that adjusts the total amount of air supplied to the incinerator body 3, a secondary air volume control valve 32 that adjusts the amount of secondary air supplied to the incinerator body 3, a sand layer temperature measuring instrument 10, and a freeboard temperature measuring instrument 11.

[0016] The control device 27 is configured by, for example, a CPU (Central Processing Unit) reading and executing a program from a storage unit. In the system shown in FIG. 1, the control device 27 grasps the fluidity state of the sand layer based on data from multiple sand layer temperature measuring devices 10, or data from multiple sand layer temperature measuring devices 10 and freeboard temperature measuring device 11, and sends control signals to the fluidization blower 21, total air flow control valve 31, and secondary air flow control valve 32 to adjust the amount of primary air, thereby maintaining the sand layer in an optimal fluidity state that does not cause poor fluidity and can reduce NO.

[0017] The piping into which combustion air supplied from the fluidized bed blower 21 is introduced includes a total air supply piping 28 arranged on the upstream side, and a primary air supply piping 29 and a secondary air supply piping 30 branching off on the downstream side of the total air supply piping 28. The fluidized bed blower 21 supplies air to the primary air supply piping 29 and the secondary air supply piping 30 via the total air supply piping 28.

[0018] The primary air supply pipe 29 supplies primary air to the sand layer section S, and the secondary air supply pipe 30 supplies secondary air to the freeboard section F. The flow rate (total air volume) of all air (all air supplied to the sand layer section S and the freeboard section F) flowing through the total air supply pipe 28 is the sum of the flow rate of primary air (primary air volume) and the flow rate of secondary air (secondary air volume) supplied to the freeboard section F. The total air volume is determined so that the furnace outlet temperature is 825 to 875°C.

[0019] Figure 4 shows the relationship between the furnace outlet temperature and the N2O concentration in the gas discharged from the furnace outlet. As shown in Figure 4, the N2O value decreases when the furnace outlet temperature is 825°C or higher, so the total air volume is determined so that the furnace outlet temperature is 825°C or higher. Furthermore, if the furnace outlet temperature exceeds 875°C, the air preheater may be damaged, and the fly ash generated from the furnace may melt and solidify, causing blockage of the exhaust gas duct. Therefore, the total amount of air is determined so that the furnace outlet temperature does not exceed 875°C.

[0020] Furthermore, Figure 5 shows the correlation between the NO concentration value at the chimney outlet and the CO concentration value at the ceramic filter outlet. As shown in Figure 5, there is a high correlation between the NO concentration value at the chimney outlet and the CO concentration value at the ceramic filter outlet (correlation coefficient 0.82). Therefore, by controlling the CO concentration to be lower, the N2O concentration can also be lowered. As described above, there is a high correlation between the NO concentration value at the chimney outlet and the CO concentration value at the ceramic filter outlet. Therefore, in the present invention, the CO concentration value is observed using a CO concentration meter, and the NO concentration value is controlled by controlling this CO concentration value.

[0021] The total air supply pipe 28 is provided with a total air amount control valve 31 that adjusts the total air amount. The secondary air supply pipe 30 is provided with a secondary air amount control valve 32 that adjusts the secondary air amount. The secondary air amount is adjusted by adjusting the secondary air amount control valve 32, and as a result, the primary air amount is adjusted. Even when the secondary air amount is adjusted by the secondary air amount control valve 32, the total air amount does not change unless the total air amount control valve 31 is operated. The total air amount control valve 31 and the secondary air amount control valve 32 are controlled by the control device 27.

[0022] The air preheater 15 preheats all the air flowing through the total air supply pipe 28. The air preheater 15 preheats the air by recovering heat from, for example, the exhaust gas discharged from the incinerator main body 3. The exhaust gas leaving the air preheater 15 is treated in a ceramic filter 33 and a smoke washing treatment tower 34, and then sent to a chimney 36 via an induced draft fan (IDF) 35.

[0023] The fluidized bed sludge incinerator 1 is equipped with a sand layer temperature measuring instrument 10 that measures the temperature Ts of the sand layer S, a freeboard temperature measuring instrument 11 that measures the temperature Tf directly above the sand layer, an exhaust gas temperature measuring instrument 13 that detects the temperature To of the exhaust gas flowing through the flue 12 immediately after it is discharged from the furnace outlet 4, and a CO concentration measuring instrument 14 that measures the CO concentration of the exhaust gas flowing through the flue 12. These measuring devices 10, 11, 13, and 14 are electrically connected to a control device 27. The control device 27 controls the total air amount control valve 31 and the secondary air amount control valve 32 based on the values ​​measured by these measuring devices.

[0024] Next, the sludge combustion process will be explained. In the following, a case where eight sand layer temperature measuring devices 10 are provided as shown in FIG. 2 will be described. The sludge M is dehydrated by a dehydration process (not shown) and supplied to the incinerator body 3 by the sludge supply device 5. In addition, combustion air is introduced into the total air supply piping 28 by the discharge pressure of the fluidization blower 21, and then heated by the air preheater 15 and supplied to the sand layer section S and the freeboard section F. The sand grains in the sand layer S, heated by the combustion air, are fluidized together with the supplied sludge M by the combustion air and the generated combustion gas, and the sludge M burns while fluidizing. Furthermore, the combustion gas rises inside the freeboard section F, and the combustion is completed by secondary air supplied through the secondary air supply piping 30. The exhaust gas after combustion is introduced into the flue 12 through the furnace outlet 4 and discharged to the exhaust gas treatment device.

[0025] Next, a method for controlling the fluidized bed sludge incinerator 1 in this embodiment will be described. First, a start-up process of the fluidized bed sludge incinerator 1 of this embodiment from start-up to stabilization of operation will be described. In the start-up process of the fluidized bed sludge incinerator 1, sludge M and primary air (air for combustion) are supplied to the incinerator body 3. In other words, secondary air is not used in the start-up process of the fluidized bed sludge incinerator 1. After the supply of sludge M and primary air, the temperature of each part of the fluidized bed sludge incinerator 1 rises, and when the temperature of each part of the fluidized bed sludge incinerator 1 has stabilized, the start-up process of the fluidized bed sludge incinerator 1 is completed.

[0026] Next, a method for controlling the fluidized bed sludge incinerator 1 after the start-up process of the fluidized bed sludge incinerator 1 will be described. During steady-state operation, the smaller the primary air volume, the lower the N2O concentration in the exhaust gas. Therefore, to reduce the N2O concentration, it is necessary to keep the primary air volume as low as possible. However, if the amount of primary air is too small, the fluidity will be poor and efficient combustion and incineration will be impossible. If it gets worse, the fluidity will stop and incineration will become impossible. Therefore, the object of the control method of the present invention is to reduce the amount of primary air to the minimum level that does not affect combustion.

[0027] In the present invention, the NO concentration is controlled by controlling the CO concentration in the exhaust gas by increasing or decreasing the amount of primary air, thereby controlling the NO concentration and achieving efficient combustion incineration. For this reason, an operational test of the fluidized bed sludge incinerator 1 is conducted in advance to determine the numerical value (lower limit) below which the CO concentration (NO concentration) exceeds a predetermined value for the temperature difference between the maximum and minimum temperatures of the sand layer, and the numerical value (upper limit) above which the fluidization state deteriorates and efficient combustion incineration cannot be achieved, and then the upper and lower limits of the sand layer temperature difference are set.

[0028] Similarly, an operational test of the fluidized bed sludge incinerator 1 is conducted in advance to determine the value (lower limit) below which the CO concentration (N2O concentration) exceeds a predetermined value for the rate of change of the temperature difference between the highest and lowest temperatures in the sand layer, and the value (upper limit) above which the rate of change of the temperature difference deteriorates and efficient combustion and incineration cannot be performed, and then the upper and lower limits for the rate of change of the temperature difference in the sand layer are set.

[0029] In the present invention, a plurality of sand layer temperature measuring devices 10 are installed in the sand layer of the fluidized bed sludge incinerator 1. Then, the temperature difference between the maximum and minimum sand layer temperatures indicated by the plurality of sand layer temperature measuring devices 10 is calculated. In the first aspect of the present invention, the amount of primary air is controlled based on this temperature difference. Specifically, when the temperature difference in the sand layer is 15°C to 30°C, the flow of the sand layer is insufficient, so the amount of primary air is controlled to be increased by 1 to 5%. On the other hand, if the temperature difference in the sand layer is 0 to 15°C, the flow of the sand layer will be too active, so the primary air volume will be controlled to be reduced by 1 to 5%. By carrying out the above control, the incinerator can be operated stably while maintaining a low N2O concentration in the exhaust gas.

[0030] In order to perform the above control, the temperature difference for starting control to increase the amount of primary air is set to a predetermined temperature between 15°C and 30°C (for example, 25°C) as the upper limit (threshold) depending on the characteristics of the fluidized bed sludge incinerator 1. In addition, the temperature difference for starting control to reduce the amount of primary air is set as a lower limit (threshold) to a predetermined temperature between 0°C and 15°C (for example, 5°C) depending on the characteristics of the fluidized bed sludge incinerator 1.

[0031] In a second aspect of the present invention, the amount of primary air is controlled based on the rate of change of this temperature difference. Specifically, when the rate of change of the temperature difference in the sand layer reaches 15°C / h to 30°C / h, the flow of the sand layer is insufficient, so the amount of primary air is controlled to increase by 1 to 5%. On the other hand, if the rate of change of the temperature difference in the sand layer is between 0°C / h and 15°C / h, the flow of the sand layer will be too vigorous, so the primary air volume will be controlled to be reduced by 1 to 5%. By carrying out the above control, the incinerator can be operated stably while maintaining a low N2O concentration in the exhaust gas.

[0032] In order to perform the above control, the rate of change of the temperature difference for starting control to increase the amount of primary air is set as an upper limit (threshold) to a predetermined temperature (e.g., 25°C) between 15°C / h and 30°C / h depending on the characteristics of the fluidized bed sludge incinerator 1. In addition, the rate of change of the temperature difference for starting control to reduce the amount of primary air is set as a lower limit (threshold) to a predetermined temperature (e.g., 50°C) between 0°C / h and 15°C / h depending on the characteristics of the fluidized bed sludge incinerator 1.

[0033] The operation of the control device 27 will now be described. First, the maximum and minimum temperature values ​​Ts indicated by the eight sand layer temperature measuring devices 10 are obtained at predetermined time intervals (for example, every minute), and the temperature difference (ΔT) is calculated. Next, when a predetermined time (t minutes: for example, 10 minutes) has passed, the temperature difference before t minutes (ΔT0) and the temperature difference after t minutes have passed (ΔT t) change rate (rate of change) [(ΔT0-ΔT t ) / t] is calculated. The system then compares data such as whether the current temperature difference is within the acceptable range, whether the rate of change of the temperature difference is positive (+) or negative (-), how large the absolute value of the rate of change is, and how long that rate of change has continued against the accumulated database to determine whether or not it is necessary to increase or decrease the amount of primary air. The control device 27 sends a signal to the total air flow control valve 31, the secondary air flow control valve 32, or the flow blower 21 to increase or decrease the amount of primary air.

[0034] [Example 1] An operational test was conducted using the fluidized bed sludge incinerator 1 shown in Figure 1, which has an inner diameter of 5.0 m and a freeboard height of 8.5 m. Silica sand was used as the fluidizing sand, and the static sand layer height was 1.0 m. The moisture content of the sludge was 75%, and the supply rate was 6 t / h. An operational test was conducted using this fluidized bed sludge incinerator 1, and the graph shown in Figure 3 was obtained showing the relationship between air volume and sand layer temperature difference and rate of change in sand layer temperature difference. In the example, the upper limit of the temperature difference of the sand layer was set to 25°C, and the lower limit of the rate of change of the temperature difference was set to 0°C / h.

[0035] In Figure 3, the difference between the maximum and minimum temperatures of the multiple sand layers reached 25°C (see the position of the short arrow in Figure 3). As a result of increasing the amount of primary air by 3%, the temperature difference was reduced as indicated by the circle in Figure 3, the poor fluidity phenomenon disappeared, and the operation of the fluidized bed sludge incinerator 1 stabilized. In one example using the rate of change of the sand layer temperature difference, at the ◎ in Figure 3 (see the position of the long arrow marked with ◎ in Figure 3), the rate of change fell below 0°C / h, so the primary air volume was reduced by 3%. As a result, it was confirmed that the sand layer temperature difference increased.

[0036] Furthermore, even if the above control is performed, there may be cases where the CO concentration in the exhaust gas discharged from the chimney becomes high (that is, the N2O concentration becomes high) for some reason. In this case, a predetermined upper limit of the CO concentration in the exhaust gas is set in advance, and when the CO concentration in the exhaust gas measured by the CO concentration measuring instrument 14 exceeds the upper limit of the CO concentration, the amount of primary air supplied to the sand layer section S is controlled to be reduced by 1 to 5%.

[0037] Moreover, an operating state that reduces the CO concentration in the exhaust gas excessively is also undesirable. Therefore, a lower limit is set for the CO concentration in the exhaust gas, and when the CO concentration in the exhaust gas measured by the CO concentration measuring instrument 14 falls below the predetermined CO concentration lower limit, the amount of primary air supplied to the sand layer section S is controlled to be increased by 1 to 5%. The regulated value for N2O concentration is 30 PPM. Therefore, to provide a margin of safety, the upper limit for control during operation may be set to, for example, less than 20 PPM, and the CO concentration corresponding to this N2O concentration (24 PPM from the correlation diagram in Figure 5) may be set as the upper limit for CO concentration.

[0038] In this embodiment of the present invention, a CO concentration measuring device 14 for measuring the CO concentration in the flue gas is provided in the flue 12, and no N2O concentration measuring device is particularly provided. As described above, there is a high correlation between CO concentration and NO concentration. Furthermore, CO concentration measuring instruments 14 are cheaper than NO concentration measuring instruments and are widely used. Therefore, the status of NO concentration can be grasped by measuring CO concentration using CO concentration measuring instrument 14 without measuring NO concentration using an NO concentration measuring instrument. Therefore, the measurement value of CO concentration measuring instrument 14 can be used for control to adjust operations. Furthermore, when it is necessary to prepare NO concentration values ​​as data, such as when it is necessary to publish exhaust gas values, the NO concentration can be calculated from the CO concentration based on the correlation data between CO concentration and NO concentration.

[0039] Below is an example in which the NO concentration and the fluidization state of the fluidized bed sludge incinerator 1 are controlled by setting upper and lower limits for the CO concentration in the exhaust gas and increasing or decreasing the amount of primary air.

[0040] [Example 2] An operational test was carried out using the same fluidized bed sludge incinerator 1 as in Example 1. The difference between the maximum and minimum temperatures of the sand layer (hereinafter referred to as the sand layer temperature difference) was set to 6°C, and the primary air volume was set to 8,400 Nm 3 / h, the CO concentration in the exhaust gas measured at the ceramic filter outlet rose to 24 PPM. At this time, the N2O concentration in the exhaust gas measured at the chimney outlet also reached the allowable value (upper control limit) of 20 PPM. Therefore, the primary air volume was increased to 8,400 Nm 3 / h to 8,000Nm 3 / h was reduced by 5.0% to lower the CO concentration to 16 PPM. As a result, the N2O concentration was reduced to 10 ppm, and the temperature difference in the sand layer was reduced to 10°C, which is within the range for a good fluidity state, enabling the incinerator to be operated in a stable manner.

[0041] [Example 3] An operation test was carried out using the same fluidized bed sludge incinerator 1 as in Example 1. Sand layer temperature difference of 20°C, primary air volume of 7,800 Nm 3 At this time, the CO concentration in the exhaust gas measured at the ceramic filter outlet was 16 PPM, and the N2O concentration in the exhaust gas measured at the chimney outlet was 10 PPM, which was below the allowable value (upper control limit: 20 PPM). However, due to a lack of primary air, the fluidity of the sand layer was insufficient. Therefore, the flow rate of the primary air was increased within the range that did not exceed the CO concentration corresponding to the N2O concentration tolerance of 20 PPM, in order to improve the fluidity of the sand layer. 3 / h to 8,200Nm 3 / h was increased by 5.0% to bring the CO concentration to 20 PPM. As a result, the N2O concentration was suppressed to 15 ppm, which is below the allowable value, and the sand layer temperature difference was reduced to 8°C, improving the sand layer fluidity and enabling the incinerator to operate stably. The results of Examples 2 and 3 are shown in Table 1.

[0042] [Table 1]

[0043] Although an embodiment of the present invention has been described above in detail with reference to the drawings, the specific configuration is not limited to this embodiment, and design changes and the like are also included within the scope that does not deviate from the gist of the present invention. [Explanation of symbols]

[0044] 1. Fluidized bed sludge incinerator 3 Incinerator body 4 Furnace outlet 5. Sludge supply device 6 Sludge inlet 7 Primary air supply section 9 Secondary air supply section 10 Sand layer temperature measuring device 11 Freeboard temperature measuring instrument 12 Flue 13 Exhaust gas temperature measuring device 14 CO concentration measuring device 15 Air preheater 17 Fluid Sand 19 Air supply nozzle 21 Flow Blower 23 Cooling blower 25 Air Cooler 27 Control Device 28 All air supply piping 29 Primary air supply piping 30 Secondary air supply piping 31 Total air flow control valve 32 Secondary air flow control valve 33 Ceramic Filter 34 Smoke washing treatment tower 35 Induced draft fan 36 Chimney F Freeboard section M sludge S sand layer

Claims

1. A fluidized bed sludge incinerator having a sand layer and a freeboard formed above the sand layer, in which sludge is burned, a plurality of temperature measuring devices provided in the sand layer portion for measuring the temperature of a plurality of locations in the sand layer; a control device that calculates the temperature difference between the maximum and minimum temperatures of the sand layer measured by the temperature measuring device and the rate of change of said temperature difference, determines the amount of primary air to be supplied to said sand layer section based on the value of the rate of change of said temperature difference, and controls the amount of primary air to be supplied to said sand layer section, so that when the rate of change of said temperature difference exceeds a predetermined upper limit value, the amount of primary air to be supplied to said sand layer section is increased, and when the rate of change of said temperature difference falls below a predetermined lower limit value, the control device controls so that the amount of primary air to be supplied to said sand layer section is decreased; A fluidized bed sludge incinerator comprising:

2. The fluidized bed sludge incinerator according to claim 1, characterized in that the control device controls the amount of primary air supplied to the sand layer to increase by 1 to 5% when the rate of change of the temperature difference exceeds the predetermined upper limit value, and controls the amount of primary air supplied to the sand layer to decrease by 1 to 5% when the rate of change of the temperature difference falls below the predetermined lower limit value.

3. 3. The fluidized bed sludge incinerator according to claim 2, wherein the predetermined upper limit is set to a value of 15°C / h or more, and the predetermined lower limit is set to a value less than 15°C / h.

4. a CO concentration measuring device for measuring the CO concentration in the exhaust gas discharged from the furnace outlet of the incinerator body of the fluidized bed sludge incinerator; The fluidized bed sludge incinerator according to any one of claims 1 to 3, characterized in that the control device is a control device that controls so as to reduce the amount of primary air supplied to the sand layer when the CO concentration in the exhaust gas measured by the CO concentration meter exceeds a predetermined CO concentration upper limit value, and to increase the amount of primary air supplied to the sand layer when the CO concentration in the exhaust gas measured by the CO concentration meter falls below a predetermined CO concentration lower limit value.

5. When the CO concentration in the exhaust gas measured by the CO concentration measuring device exceeds a predetermined CO concentration upper limit value, the control device reduces the amount of primary air supplied to the sand layer by 1 to 5%, The fluidized bed sludge incinerator according to claim 4, characterized in that the control device controls the amount of primary air supplied to the sand layer to be increased by 1 to 5% when the CO concentration in the exhaust gas measured by the CO concentration measuring device falls below a predetermined CO concentration lower limit value.

6. 6. The fluidized bed sludge incinerator according to claim 4, wherein the predetermined CO concentration upper limit value is 10 to 20 ppm, and the predetermined CO concentration lower limit value is 0 to 10 ppm.

7. 1. An automatic combustion control method for a fluidized bed sludge incinerator that has a sand layer and a freeboard formed above the sand layer and burns introduced sludge, comprising: a plurality of temperature measuring devices for measuring the temperature of the sand layer at different positions are provided in the sand layer section; The method for automatic combustion control of a fluidized bed sludge incinerator comprises calculating the temperature difference between the maximum and minimum temperatures of the sand layer measured by the temperature measuring device and the rate of change of said temperature difference, and controlling the amount of primary air supplied to said sand layer to increase if the rate of change of said temperature difference exceeds a predetermined upper limit value, and decreasing the amount of primary air supplied to said sand layer if the rate of change of said temperature difference falls below a predetermined lower limit value.

8. The automatic combustion control method for a fluidized bed sludge incinerator according to claim 7, characterized in that when the rate of change of the temperature difference exceeds the predetermined upper limit, the amount of primary air supplied to the sand layer is increased by 1 to 5%, and when the rate of change of the temperature difference falls below the predetermined lower limit, the amount of primary air supplied to the sand layer is decreased by 1 to 5%.

9. The automatic combustion control method for a fluidized bed sludge incinerator according to claim 8, characterized in that the predetermined upper limit value is set to a value of 15°C / h or more, and the predetermined lower limit value is set to a value less than 15°C / h.

10. The CO concentration in the exhaust gas discharged from the furnace outlet of the incinerator body of the fluidized bed sludge incinerator is measured with a CO concentration measuring device; When the CO concentration in the exhaust gas measured by the CO concentration measuring device exceeds a predetermined CO concentration upper limit value, the amount of primary air supplied to the sand layer portion is reduced, The automatic combustion control method for a fluidized bed sludge incinerator according to any one of claims 7 to 9, characterized in that when the CO concentration in the exhaust gas measured by the CO concentration measuring device falls below a predetermined CO concentration lower limit value, the amount of primary air supplied to the sand layer section is increased.

11. When the CO concentration in the exhaust gas exceeds a predetermined CO concentration upper limit value, the amount of primary air supplied to the sand layer is reduced by 1 to 5%; The automatic combustion control method for a fluidized bed sludge incinerator according to claim 10, characterized in that when the CO concentration in the exhaust gas falls below a predetermined CO concentration lower limit, the amount of primary air supplied to the sand layer is increased by 1 to 5%.

12. The automatic combustion control method for a fluidized bed sludge incinerator according to claim 10 or 11, characterized in that the predetermined CO concentration upper limit value is 10 to 20 PPM, and the predetermined CO concentration lower limit value is 0 to 10 PPM.

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