Method and control device for reducing N2O emissions in exhaust gas

Abstract

To provide an operation method in a fluidized incinerator, capable of securing N2O emission without increasing costs by improving heat resistance and the like of incineration facilities, in keeping an incineration temperature necessary for N2O decomposition, and a device therefor.SOLUTION: A method of reducing a discharge amount of N2O in an exhaust gas is provided to control a fluidized incinerator 2 for incinerating an incineration object which is mainly sludge. In the method of reducing the discharge amount of N2O in the exhaust gas, an amount of exhaust gas discharged from the fluidized incinerator is calculated or the amount of exhaust gas is directly measured on the basis of the gas generating in the fluidized incinerator, a superficial velocity of the fluidized incinerator is calculated on the basis of the calculated or measured amount of exhaust gas, and the superficial velocity is controlled by adjusting a pressure of a compression gas supplied from a supercharger 50. A control device 90 is operated on the basis of a control program for executing the reduction of the discharge amount of N2O.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to the control of a fluidized bed incinerator, which controls the fluidization state of a fluidized bed material such as sludge that flows within the incinerator, and in particular to a method and apparatus for reducing emissions of N2O, a greenhouse gas, when adjusting the combustion gas residence time within a fluidized bed incinerator. [Background technology]

[0002] A fluidized bed incinerator is an incinerator that uses air pumped in from the bottom of the furnace to fluidize a fluidized bed (such as sand) containing sand as a fluidizing medium, and then stirs and incinerates the materials to be incinerated, such as sewage sludge or municipal waste, that are placed in the heated fluidized bed. The fluidization state within a fluidized bed incinerator varies depending on the air supplied to the furnace (also referred to as supply air, combustion air, fluidizing air, or preheated air), the amount of materials to be incinerated, auxiliary fuel, etc., as well as the temperature and pressure within the furnace. Stabilizing the fluidization state and optimizing the combustion state is important for increasing the combustion efficiency of the materials to be incinerated. In addition, in order to prevent global warming, it is necessary to reduce emissions of N2O (nitrous oxide), a greenhouse gas that is produced from exhaust gases when incinerating organic components contained in materials to be incinerated.

[0003] For example, in a fluidized bed incinerator, a method has been proposed in which the amount of air supplied into the furnace to fluidize the bed material is adjusted according to the brightness inside the furnace, the amount of material to be incinerated, the temperature, the oxygen concentration, or the pressure inside the furnace (see Patent Document 1). In addition, a method has been proposed for stabilizing combustion in a fluidized bed incinerator by estimating the increase or decrease in moisture content of sewage sludge cake based on the oxygen concentration of the exhaust gas and the moisture concentration in the upper part of the furnace, and adjusting the amount of air supplied to the furnace, the temperature inside the furnace, the amount of material to be incinerated supplied to the furnace, etc. based on the estimated results (see Patent Document 2). To reduce exhaust gas emissions, particularly N2O (hereinafter referred to as N2O) and NOx, a method is known in which a slurry mixture of an ammonia-based reducing agent and a porous fluidized medium is injected into a furnace (see Patent Document 3). [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Patent No. 3108742 [Patent Document 2] Japanese Patent Application Laid-Open No. 2004-125332 [Patent Document 3] Patent No. 5640120 [Patent Document 4] Japanese Patent Publication No. 2020-159655

[0005] The amount of sewage sludge generated is increasing year by year, and about 70% of it is incinerated. Sludge has a much higher nitrogen content than other fuels when burned, and there are concerns that N2O will be emitted during the incineration process. The supercharged fluidized bed incinerator system creates a high temperature zone through combustion under pressure, which can reduce the N2O contained in combustion exhaust gas. In a turbocharged fluidized bed incinerator, the fuel (sludge, etc.) to be burned in the fluidized bed is applied to the furnace top and furnace outlet, and burned at a temperature of, for example, 870 to 880°C, decomposing nitrous oxide (N2O), a greenhouse gas. Note that the greenhouse effect of N2O is 298 times that of CO2. The incinerator temperature is regulated by combustion using auxiliary fuel (assisted combustion state) to maintain the temperature inside the furnace according to the characteristics of the dewatered sludge, or by combustion without supplying auxiliary fuel (self-combustion state) when the dewatered sludge has low moisture content and is easy to burn, and when the temperature inside the furnace rises, water is injected into the furnace to cool it down (spontaneous combustion state). Summary of the Invention [Problem to be solved by the invention]

[0006] In this type of fluidized bed incinerator, superficial velocity is one of the indicators that indicates the fluid flow state within the incinerator. For example, when designing a fluidized bed incinerator, a superficial velocity appropriate for operation at a specified incineration load is set, and the size of the incinerator and the particle size of the bed material are determined so that the materials to be incinerated are incinerated at the set superficial velocity. Since the fluid flow state within the incinerator is correlated with the superficial velocity within the incinerator, if the superficial velocity during operation, which is not the design value, can be determined, it is possible to indirectly confirm the fluid flow state. For example, if the superficial velocity falls below the appropriate range and the bed material is not sufficiently fluidized, the combustion efficiency will decrease, and furthermore, the ash generated by combustion will be difficult to discharge from the furnace, resulting in an increase in the bed material containing ash in the fluidized sand inside the furnace.

[0007] On the other hand, if the superficial velocity exceeds the appropriate range and the bed material becomes excessively fluid, in addition to the ash that is discharged well, the bed material (fluid sand) will be scattered outside the furnace, resulting in a decrease in the bed material in the furnace. The withdrawal of the increased bed material from the furnace and the replenishment of the decreased bed material to the furnace increase the operating costs of the fluidized bed incinerator. Therefore, it is desirable to operate the fluidized bed incinerator so that the superficial velocity falls within the appropriate range.

[0008] However, the superficial velocity in an incinerator varies depending not only on the amount of air supplied to the incinerator but also on the amount of gas generated by the combustion of the material to be incinerated, auxiliary fuel, and water injection into the incinerator. For this reason, it is difficult to accurately represent the flow state inside the incinerator using the superficial velocity calculated using only the amount of air supplied.

[0009] In Patent Document 1, the controllable superficial velocity range is set at the time of design based on the results of controlling each element, but as mentioned above, it is difficult to measure the actual superficial velocity, and therefore this is not implemented.

[0010] In order to reduce the amount of N2O emitted from exhaust gases, N2O is decomposed at high temperatures. In the embodiments described below, the reduction of N2O emissions will be described as an example.

[0011] Figure 3 is a diagram illustrating an example of the correlation between maximum furnace temperature and N2O emission coefficient, and is an approximation of the correlation equation, with maximum furnace temperature [°C] on the horizontal axis and N2O emission coefficient per dry weight of dehydrated cake [kg-N2O / t-DS] on the vertical axis. As shown in Figure 3, N2O decomposition is correlated with furnace temperature.

[0012] However, if the temperature is increased to further decompose N2O, the amount of N2O reduction decreases, as is clear from the approximate curve in Figure 3. Therefore, it becomes difficult to meet the demand for reduced N2O emissions simply by increasing the furnace temperature.

[0013] Even if it is possible to accelerate the decomposition of NO by further increasing the temperature inside the furnace, there is a high possibility that adverse effects will occur due to the generation of more localized high temperature areas, and that adverse effects will occur due to the melting and adhesion of fly ash caused by the higher temperature of the exhaust gas entering the air preheater and the higher temperature at the furnace outlet. This will increase the costs of improving the heat resistance of the incineration equipment and taking measures against the melting and adhesion of fly ash, and will require the implementation of separate operational management measures for NO decomposition.

[0014] The object of the present invention is to provide an operating method and apparatus for a fluidized bed incinerator that ensures NO emissions without increasing costs by improving the heat resistance of the incineration equipment when maintaining the incineration temperature required for NO decomposition, and more specifically, to provide an NO emission reduction control method and control apparatus that realizes an operating index for adjusting the gas residence time in the fluidized bed incinerator.

[0015] Furthermore, in supercharged fluidized bed incineration, which incinerates sludge with a low moisture content, under natural conditions, the temperature inside the furnace rises, the amount of water injected increases, and the residence time of the exhaust gas inside the furnace shortens, resulting in an increase in N2O. Therefore, the objective is to increase the pressure with a supercharger to suppress the superficial velocity inside the furnace (hereinafter referred to as the space rate), thereby increasing the residence time of the exhaust gas generated inside the furnace and thereby suppressing N2O emissions. [Means for solving the problem]

[0016] The N2O reduction technology according to the present invention, which is intended to achieve the above-mentioned objective, is characterized by focusing on the residence time of gas generated in the furnace in addition to the temperature condition, and using the residence time in the furnace as an indicator of N2O reduction.

[0017] As mentioned above, it was thought that the suppression of NO emissions was correlated with the maximum temperature of the exhaust gas in the furnace, but research by the present inventors has revealed that there is also a correlation with the gas residence time in the furnace. That is, as will be described later, we have clarified an inverse proportional relationship in which NO emissions are suppressed as the gas residence time in the furnace increases. Note that data suggesting the above correlation can also be found in Figure 3 of Patent Document 3.

[0018] There are two ways to increase the gas residence time in the incinerator: (1) increasing the size of the incinerator or (2) decreasing the exhaust gas space rate within the incinerator. The space rate is calculated by calculating the gas generation rate from the fluidized incinerator based on the supply rates of the sludge and other incineration materials (sludge supply volume meter 82 (process value of F3)) from the sludge supply device 10 shown in Figure 1, the water (water supply volume meter 83 (process value of F4)) from the water supply device 15 that injects water into the incinerator, the fuel (fuel supply volume meter 84 (process value of F5)) from the fuel supply device 20, and the combustion air (air preheater air volume meter 27 (process value of F2)) to the fluidized incinerator 2. The exhaust gas generation rate from the fluidized incinerator 2 can be measured directly. However, if measurement is difficult due to the influence of ash in the exhaust gas, the exhaust gas volume can be measured downstream from the outlet of the dust collector 40 (e.g., supply line 41).

[0019] When calculating the space rate from each supply amount indicated by each measuring device, the mass flow rate is first calculated from each supply amount, and then converted to a volumetric flow rate to calculate the gas generation rate, thereby calculating the space rate. The gas generation rate of an incineration object is calculated, for example, by calculating the gas generation rate when the incineration object is incinerated based on the moisture content, organic component rate, and elemental composition obtained by measuring devices and analytical work. It is acceptable to calculate the gas generation rate of an incineration object using values ​​obtained by statistically organizing values ​​obtained by daily measuring devices and analytical work, rather than using real-time measurements.

[0020] Since the above (1) leads to an increase in equipment costs, it is usually dealt with by the above (2). In order to reduce the space rate of exhaust gas in the furnace, it is effective to increase the pressure inside the furnace if the mass flow rate is constant. In other words, by extending the residence time of the exhaust gas generated in the furnace, the space rate for suppressing the decomposition of N2O can be maintained.

[0021] Thus, NO decomposition occurs in proportion to the gas residence time in a high-temperature field, in addition to the temperature correlation shown in Figure 3. In the present invention, NO is reduced by adopting an operating method that ensures sufficient residence time in the furnace, using the speed at which gas generated in the furnace passes through the furnace (space rate) as an index.

[0022] A similar technique is described in Patent Document 4, but the present invention is characterized in that it is a configuration and method for reducing NO by applying the above-mentioned "adjustment by operating pressure" technology to space rate management and adjustment aimed at the gas residence time in the high-temperature furnace during NO decomposition.

[0023] In the present invention, (a): For example, in a supercharged fluidized bed furnace for incinerating sludge with a low moisture content, when the furnace is in a self-combustion state, the temperature inside the furnace rises and the amount of water injected increases, shortening the residence time in the high-temperature area inside the furnace and increasing NO emissions. Therefore, by increasing the pressure with a supercharger and suppressing the space rate inside the furnace, the residence time is increased and NO emissions are reduced.

[0024] Also, (b): In order to maintain the increased pressure, a portion of the fluidized air is discharged through the control valve 49 shown in Figure 1, which is located in the excess air release path. If the excess air is not released, poor fluidity will occur in the fluidized bed 3 inside the fluidized incinerator, and the space rate will become so small that it will lead to incomplete combustion of the materials to be incinerated. Therefore, the excess air is released to maintain the increased pressure and achieve an appropriate space rate.

[0025] Representative features of the N2O emission reduction control means according to the present invention are as follows: Note that, to facilitate understanding of the invention, the reference numerals used in the drawings of the embodiments described below are used for each component, but the present invention is not limited to the specific components indicated by these reference numerals.

[0026] Method for reducing N2O emissions in exhaust gas from a fluidized bed incinerator that mainly incinerates sludge to Regarding this, please see [1] below. 、 [ 2 ] as follows. [1] A method for reducing NO emissions in exhaust gas for controlling a fluidized bed incinerator that incinerates materials to be incinerated, with sludge being the main incineration target, comprising: calculating the amount of exhaust gas discharged from the fluidized bed incinerator based on the gas generated in the fluidized bed incinerator; or directly measuring the amount of exhaust gas; calculating the superficial velocity of the fluidized bed incinerator based on the calculated or measured amount of exhaust gas; and adjusting the pressure of compressed air supplied from a turbocharger to control the superficial velocity. In controlling the superficial velocity, the superficial velocity and the correlation equation calculation N 2 O and N 2 In relation to the deviation of the O measurement value, the superficial velocity is controlled to a value where the deviation is 0 or less. A method for reducing N2O emissions in exhaust gas, characterized by: [2] The superficial velocity is compared with a set minimum value, and if the superficial velocity falls below the minimum value, the opening of a control valve in the exhaust gas bypass passage of the turbocharger is increased, the amount of exhaust gas sent to the turbocharger is reduced, the rotation speed of the turbocharger is lowered, and the opening of the excess air control valve is reduced, Compressed air is supplied from the turbocharger The method for reducing NO emissions in exhaust gas according to [1], characterized in that the pressure downstream of the supply passage is maintained, the superficial velocity is compared with a set maximum value, and if the superficial velocity exceeds the maximum value, the aperture of a control valve in the exhaust gas bypass passage of the turbocharger is reduced, the amount of exhaust gas sent to the turbocharger is increased, the rotation speed of the turbocharger is increased, and the aperture of the surplus air control valve is increased, thereby maintaining the pressure downstream of the supply passage.

[0027] Fluidized bed incinerators that mainly incinerate sludge A control device for controlling Regarding this, please see below 3 〕 、 [4 ] as follows. [ 3 〕For controlling a fluidized bed incinerator that incinerates materials to be incinerated, the main incineration target of which is sludge Control device The incinerator operates based on a control program for reducing N2O emissions in exhaust gas, which is characterized by calculating the amount of exhaust gas discharged from the fluidized bed incinerator based on the gas generated in the fluidized bed incinerator, or directly measuring the amount of exhaust gas, calculating the superficial velocity of the fluidized bed incinerator based on the calculated or measured amount of exhaust gas, and controlling the superficial velocity by adjusting the pressure of compressed air supplied from a turbocharger. In controlling the superficial velocity, the superficial velocity and the correlation equation calculation N 2 O and N 2 In relation to the deviation of the O measurement value, the superficial velocity is controlled to a value where the deviation is 0 or less. A control device. [ 4 ] the superficial velocity is compared with a set minimum value, and if the superficial velocity falls below the minimum value, the opening of a control valve in the exhaust gas bypass passage of the turbocharger is increased, the amount of exhaust gas sent to the turbocharger is reduced, the rotation speed of the turbocharger is lowered, and the opening of the excess air control valve is reduced, Compressed air is supplied from the turbocharger The pressure downstream of the supply passage is maintained, the superficial velocity is compared with a set maximum value, and if the superficial velocity exceeds the maximum value, the opening of a control valve in the exhaust gas bypass passage of the turbocharger is reduced, the amount of exhaust gas sent to the turbocharger is increased, the rotation speed of the turbocharger is increased, and the opening of the excess air control valve is increased, thereby maintaining the pressure downstream of the supply passage. 3 ] A control device according to the above. [Effects of the Invention]

[0028] According to the present invention, in order to maintain the incineration temperature required for N2O decomposition, the heat resistance of the fluidized bed incineration equipment can be improved, thereby ensuring the amount of N2O emissions without increasing costs, and achieving the following effects.

[0029] When dewatered sludge (cake) with low moisture content and a high solid content is incinerated, the amount of N2O generated correlates with the amount of solids. Dewatered sludge with low moisture content and a high solid content has a high calorific value, making it prone to spontaneous combustion. When spontaneous combustion occurs, the temperature inside the furnace tends to rise, which increases the amount of water injected into the furnace. Injecting water into the furnace suppresses the temperature inside the furnace, but the amount of exhaust gas increases, which increases the space rate inside the furnace and shortens the gas residence time in the high-temperature area inside the furnace. This results in a decrease in N2O decomposition, as described below. Therefore, by increasing the operating pressure, slowing the space rate, and increasing the exhaust gas residence time, the N2O decomposition reaction is maintained and N2O emissions do not increase. [Brief explanation of the drawings]

[0030] [Figure 1] 1 is a schematic diagram showing an example of an incineration system including a control device for a fluidized incinerator according to a first embodiment. FIG. [Figure 2] FIG. 2 is a cross-sectional view showing an example of the structure of an air preheater. [Figure 3] FIG. 10 is a diagram illustrating an example of the correlation between the maximum furnace temperature and the N2O emission coefficient. [Figure 4] FIG. 4 is a diagram illustrating the discrepancy [%] between the calculated N2O obtained from the correlation equation in FIG. 3 and the measured N2O value of the exhaust gas measured by an analyzer with respect to the furnace space rate [m / sec]. [Figure 5] FIG. 2 is an explanatory diagram showing the flow of calculations executed by the control device. DETAILED DESCRIPTION OF THE INVENTION

[0031] Hereinafter, this embodiment will be described with reference to the drawings. The figure is a schematic diagram showing an example of an incineration system including a control device for a fluidized bed incinerator in the first embodiment, and FIG. 2 is a cross-sectional view showing an example of the structure of an air preheater. Hereinafter, this embodiment will be described with reference to the drawings. FIG. 1 shows an example of an incineration system including a control device for a fluidized bed incinerator according to the first embodiment.

[0032] The incineration system 1 shown in Figure 1 consists of a fluidized bed incinerator 2, a sludge (cake) supply device 10, a water supply device 15, a fuel supply device 20, an air preheater 30, a dust collector 40, a turbocharger 50, a startup blower 60, a white smoke prevention fan 70, and a control device 90. The white smoke prevention fan 70 sends the air it takes in to the white smoke prevention device 75 located downstream, and the white smoke prevention device 75 heats the air sent from the white smoke prevention fan 70 by heat exchange with the exhaust gas discharged from the turbocharger 50, which is supplied via the supply path 42. The heated air is sent to the flue gas treatment tower 80 located downstream. The incineration system 1 also has thermometers 23 and 24, a pressure gauge 25, air preheater air volume measuring instruments 26 and 27, and a turbocharger rotation speed measuring instrument 28. F2 shown in the air preheater air amount measuring instrument 27 in FIG. 1 represents the amount of compressed air supplied from the turbocharger 50 to the air preheater 30.

[0033] For example, in an embodiment of the present invention, the fluidized incinerator 2 is a turbocharged fluidized incinerator. The fluidized incinerator 2 supplies heated compressed air to the incinerator 2 and burns the materials to be incinerated in the incinerator 2 under high temperature and pressure conditions, thereby increasing the combustion rate and reducing the amount of emissions of harmful substances such as NO. In the following description, the fluidized bed incinerator 2 will also be simply referred to as the incinerator 2.

[0034] The thick solid lines with arrows indicate supply paths (supply pipes) for sludge (cake), auxiliary fuel, air, water, or exhaust gas, and the dashed lines with arrows indicate bypass paths. Thin solid lines with arrows (for example, <1> a line connecting the pressure gauge 25 to the control valve 48 (CV4), <2> a line connecting the control valve 48 (CV4) to the turbocharger rotation speed measuring device 28, <3> a line connecting the turbocharger rotation speed measuring device 28 to the air preheater air amount measuring device 27, <4> a line connecting the air preheater air amount measuring device 27 to the control valve 49 (CV5), <5> a line connecting the thermometer 23 to the control valve 17 (CV2) and the control valve 22 (CV1), <6> a line connecting the control valve 17 (CV2) to the thermometer 24, <7> a line connecting the thermometer 24 to the control valve 47 (CV3), <8> a line connecting the air preheater air amount measuring device 26 to the control valve 47 (CV3), etc.) indicate signal lines that send control signals from the control device to these control valves. For example, the control device 90 receives a pressure value from the pressure gauge 25, sends an opening command signal to the control valve 48 (CV4) based on the pressure value, and adjusts the opening of the control valve 48.

[0035] The fluidized bed incinerator 2 is equipped therein with a fluidized bed 3, a preheated air intake 4, and a startup burner 5. It also has a sludge inlet (not shown) for taking in sludge supplied from a supply line (sludge supply pipe) 11 connected to a sludge (cake) supply device 10, a water (water injection) intake (not shown) for taking in water (water injection) supplied from a supply line (water supply pipe) 16 connected to a water supply device 15, and a fuel intake (not shown) for taking in auxiliary fuel supplied from a supply line (fuel supply pipe) 21 connected to a fuel supply device 20. The sludge (cake) supplying device 10 sequentially supplies sewage sludge cakes, which have been sent from a sewage treatment facility and stored in a hopper (not shown), from a supply pipe 11 to the incinerator 2.

[0036] The water supply device 15 adjusts the combustion temperature inside the incinerator 2 by sending water (water injection) into the incinerator 2 from the connected supply pipe 16, and the fuel supply device 20 adjusts the combustion temperature inside the incinerator 2 by sending auxiliary fuel into the incinerator 2 from the connected supply pipe 21. The water supply pipe 16 is provided with a control valve 17 (CV2), and the fuel supply pipe 21 is provided with a control valve 22 (CV1). The control valve 17 (CV2) and the control valve 22 (CV1) are connected to a control device 90, and the opening degree thereof is adjusted in response to a control signal output from the control device 90.

[0037] The thermometer 23 measures the temperature of the fluidized bed 3 provided in the fluidized incinerator 2. The thermometer 23 is connected to the control device 90 and outputs the measured temperature value to the control device 90. The thermometer 24 measures the temperature of the preheated air supplied from the air preheater 30 into the fluidized bed incinerator 2. The thermometer 24 is connected to the control device 90 and outputs the measured temperature value to the control device 90.

[0038] The pressure gauge 25 measures the pressure of the exhaust gas inside the fluidized bed incinerator 2. The pressure gauge 25 is connected to the control device 90 and outputs the measured pressure value to the control device 90. The air preheater air amount measuring instrument 26 measures the amount of compressed air supplied from the turbocharger 50 to the air preheater 30. The air preheater air amount measuring instrument 26 is connected to the control device 90 and outputs the measured compressed air amount value to the control device 90.

[0039] The air preheater air amount measuring instrument 27 measures the amount of compressed air supplied from the turbocharger 50. The air preheater air amount measuring instrument 27 is connected to the control device 90 and outputs the measured compressed air amount value to the control device 90. The rotation speed measuring device 28 measures the rotation speed of the supercharger 50. The rotation speed measuring device 28 is connected to the control device 90 and outputs the measured rotation speed value to the control device 90.

[0040] FIG. 2 is a cross-sectional view showing an example of the structure of an air preheater. The air preheater 30 is composed of a cylindrical housing 30a, and the inside of the housing 30a is divided by a partition plate 30c to provide an upper parallel flow heat exchange chamber 30d and a lower counter flow heat exchange chamber 30e. 30f is the high temperature side tube plate, 30g is the low temperature side tube plate, 30h is the heat transfer tube, 30i is the baffle plate, 30j is the exhaust gas discharge chamber, 30k is the compressed air introduction header that sends compressed air to the upper parallel flow type heat exchange chamber 30d, 30m is the compressed air introduction header that sends compressed air to the lower counter flow type heat exchange chamber 30e, 30n is the thermal fluid discharge header, F1 is the high temperature exhaust gas, and F2 is the low temperature exhaust gas. The high-temperature exhaust gas F1 supplied from the fluidized bed incinerator 2 to the air preheater 30 via the supply line 58 is separated from the upper heat exchange chamber 30d by the high-temperature side tube plate 30f, and the exhaust gas discharge chamber 30j is separated from the upper heat exchange chamber 30d and the lower countercurrent heat exchange chamber 30e by the low-temperature side tube plate 30g. A large number of heat transfer tubes 30h are installed in the heat exchange chambers (heat exchange chambers 30d and 30e), and the upper and lower ends of the heat transfer tubes 30h are connected to the high-temperature side tube plate 30f and the low-temperature side tube plate 30g, respectively. The high-temperature exhaust gas F1 that flows into the heat exchange chambers (heat exchange chambers 30d and 30e) through the heat transfer tubes 30h is sent from the fluidized bed incinerator 2 via a supply path 58. A partition plate 30c is attached to the middle of the heat exchange chamber, dividing the heat exchange chamber into an upper heat exchange chamber 30d and a lower heat exchange chamber 30e. Several baffle plates 30i are arranged in the upper heat exchange chamber 30d and the lower heat exchange chamber 30e.

[0041] In the upper parallel flow heat exchange chamber 30d, the air and exhaust gas flow in the same direction, and the heat exchange volume is small, so the air discharged from the air preheater is difficult to heat up. On the other hand, in the lower counter flow heat exchange chamber 30e, the air and exhaust gas flow in opposite directions, and the heat exchange volume is large, so the air coming out is easily heated. At the thermal fluid discharge header 30n at the position where the supply line 29 is connected, the preheated air flowing from the upper parallel flow heat exchange chamber and the preheated air flowing from the lower counter flow heat exchange chamber are mixed, and the mixed preheated air is supplied to the incinerator.

[0042] In the air preheater 30, which is an embodiment of the present invention, heat is exchanged between exhaust gas sent from the fluidized bed incinerator 2 via the supply line 58 and compressed air sent from the turbocharger 50 via the supply line 56, the branch supply line 56a, and the branch supply line 56b. The heat-exchanged air is then supplied from the preheated fluid discharge header 30n through the supply path 29 to the incinerator 2 through the preheated air intake 4.

[0043] The dust collector 40 separates and recovers solid components such as ash contained in the exhaust gas discharged from the air preheater 30 and fed through the supply path 31, and feeds the exhaust gas from which solid components such as ash have been removed to the turbocharger 50 through the supply path 41. The fed exhaust gas is then fed from the turbocharger 50 to the white smoke preventive device 75 through the supply path 42.

[0044] The turbocharger 50 has a turbine 52 and a compressor 53 connected to a common rotating shaft 51. The turbine 52 receives exhaust gas sent from the dust collector 40 via the supply path 41 to the turbocharger 50 and rotates at high speed, thereby rotating the compressor 53 at high speed. The compressor 53 compresses the air taken in by the turbocharger 50 and sends the compressed air to the air preheater 30 via the supply path 56, the branch supply path 56a, and the branch supply path 56b. In the air preheater 30, heat is exchanged between the exhaust gas and the compressed air, and the heated compressed air is sent to the preheated air intake 4 of the incinerator 2 via the supply path 29.

[0045] A control valve 47 (CV3) is provided in the supply path 56 between the branch supply path 56a and the branch supply path 56b to adjust the amount of compressed air supplied to the upper heating chamber 30d and the lower heating chamber 30e of the air preheater 30. The control valve 47 (CV3) is connected to a control device 90, and its opening is adjusted in response to a control signal output from the control device 90. By adjusting this opening, the amount of compressed air supplied to the branch supply passage 56a supplying air to the upper side of the air preheater 30 and the branch supply passage 56b supplying air to the lower side of the air preheater 30 is adjusted.

[0046] A startup blower 60 supplies air taken in at the start-up of the incineration system 1 from a supply path 61 to the air supply path 56 and from a supply path 62 to the turbocharger 50. Reference numeral 63 denotes a check valve provided in the supply path 62. After startup, when the stage has come where the exhaust gas from the fluidized bed incinerator 2 can secure fluidizing air from the compressor 53 of the turbocharger 50, the supply of atmospheric air (air) from the startup blower 60 is stopped, and switching is made so that atmospheric air is supplied to the turbocharger 50 from a supply line 65. 66 is a control valve provided in the supply line 65, and is connected to a control device 90, and its opening is adjusted in response to a control signal output from the control device 90.

[0047] The white smoke prevention fan 70 sends the air it has taken in to the white smoke prevention device 75 via a supply path 71. The white smoke preventer 75 heats the air sent in from the white smoke preventive fan 70, which takes in the air, by heat exchange with the exhaust gas discharged from the turbocharger 50 and supplied via the supply path 42. The heated air is sent to the flue gas treatment tower 80. In the flue gas treatment tower 80, air pollutants such as sulfur oxides and soot contained in the flue gas are removed from the flue gas.

[0048] A bypass passage 43 provided between the supply passage 41 and the supply passage 42 is provided with a control valve 48 (CV4) for adjusting the amount of exhaust gas supplied from the turbocharger. The control valve 48 (CV4) is connected to a control device 90, and the opening degree thereof is adjusted in response to a control signal output from the control device 90. The amount of exhaust gas sent from the supply path 41 to the turbocharger 50 is adjusted by adjusting this opening degree. For example, when the opening degree of the control valve 48 (CV4) is increased, part of the exhaust gas sent to the turbocharger 50 from the supply path 41, which supplies exhaust gas from the dust collector 40 to the turbocharger, flows to the supply path 42, which supplies exhaust gas from the turbocharger 50 to the white smoke suppressor 75, and the amount of exhaust gas sent from the supply path 41 to the turbocharger 50 is reduced. Then, according to the amount of exhaust gas sent from the supply path 41 to the turbocharger 50, the pressures in the compressed air supply path downstream of the compressor 53, the air preheater 30, and the incinerator 2 are adjusted. For example, when it is desired to increase the pressure of the supply air in the air preheater 30, the control valve 48 (CV4) is closed to increase the rotation speed of the turbocharger 50. Conversely, when it is desired to decrease the pressure of the supply air, the opening of the control valve 48 (CV4) is increased to decrease the rotation speed of the turbocharger.

[0049] Further, a bypass passage 53 provided between the air supply passage 56 and the supply passage 71 is provided with a control valve 49 (CV5) for adjusting the amount of excess air. The surplus air control valve 49 (CV5) is connected to a control device 90, and the opening degree thereof is adjusted in response to a control signal of an opening degree command outputted from the control device 90. When adjusting the pressure of the supply air, the pressure of the compressed air sent from the supercharger 50 to the supply passage 56 is adjusted by adjusting this opening, and the amount of compressed air is adjusted.

[0050] For example, when the mass flow rate of compressed air is constant, the volumetric flow rate decreases when the pressure is high, so by increasing the opening of the surplus air control valve 49 (CV5) to release the surplus air from the bypass path 53 to the supply path 71 and releasing the pressure, the volumetric flow rate of compressed air sent from the supply path 56 to the air preheater 30 is increased. On the other hand, when the pressure is low, the volumetric flow rate increases, so by reducing the opening of the surplus air control valve 49 (CV5) to maintain the pressure without releasing the surplus air from the bypass path 53 to the supply path 71, the volumetric flow rate of compressed air sent from the supply path 56 to the air preheater 30 is reduced. In other words, the amount of fluidized air is affected by changes in the volumetric flow rate that accompany changes in the pressure of the fluidized air, so by adjusting the opening of the excess air control valve 49 (CV5), the amount of fluidized air can be kept within a certain range, the fluidized state of the fluidized bed in the fluidized incinerator can be stabilized, and the combustion state can be made appropriate.

[0051] The control device 90 includes, for example, a PLC (Programmable Logic Controller) and operates based on a control program executed by the PLC. The control device 90 receives signals from various sensors (such as a thermometer, a pressure gauge, an air preheater air volume measuring device, and a turbocharger rotation speed measuring device), and sends control signals corresponding to the received signals to various devices (control valves) to control the various devices using a built-in control program.

[0052] A first calculation unit 91 calculates the amount of exhaust gas discharged from the fluidized incinerator 2 based on the supply amounts of multiple types of supplies from the incineration material supply device 10, water supply device 15, fuel supply device 20, and air supply sources such as turbocharger 50, which are supplies supplied to the fluidized incinerator 2. A second calculation unit 92 calculates the space rate of the fluidized incinerator based on the calculated amount of exhaust gas.

[0053] Figure 4 illustrates the percentage difference between the calculated N2O value obtained from the correlation equation in Figure 3 and the measured N2O value of the exhaust gas measured by an analyzer as a function of the furnace space rate [m / sec]. As shown in Figure 4, the percentage difference between the calculated N2O value from the correlation equation and the measured N2O value as the furnace space rate [m / sec] increases or decreases can be approximated by a linear curve. The difference disappears when the furnace space rate is around 0.73 m / sec, and the calculated N2O value from the correlation equation matches the measured N2O value. Above this range, the difference increases in the positive direction, and the measured N2O value is greater than the calculated N2O value. This means that at higher space rates, the gas residence time in the furnace decreases, resulting in an increase in the actual amount of N2O emitted. On the other hand, when the furnace space rate is smaller than around 0.73 m / sec, the deviation becomes larger in the negative direction, and the measured N2O value becomes smaller than the calculated N2O value, which means that when the space rate is small, the gas residence time in the furnace increases, and the actual amount of N2O emitted decreases. Therefore, by keeping the furnace space rate [m / sec] as small as possible, N2O emissions can be suppressed.

[0054] Fig. 5 is a flowchart illustrating an example of N2O emission suppression by the control device 90 shown in Fig. 1. The control device 90 repeatedly executes this process at predetermined intervals, a typical example of which is every few seconds.

[0055] When the incinerator is operating and it reaches the start time of the above-mentioned predetermined cycle, this control starts (START). Once it starts, first, the exhaust gas mass flow rate is measured or calculated (step 1, hereinafter referred to as S1).

[0056] Next, the exhaust gas volume flow rate is calculated from the furnace temperature T3 and the furnace pressure P1 (S2), and subsequently, the furnace space rate S1 is calculated (S3).

[0057] The furnace space rate S1 is compared with the set minimum value S1min (S4). If S1 < S1min, an operation to decrease P1 is executed (S5). The operation to decrease P1 is to increase the opening degree of the regulating valve 48 in the bypass path 43, reduce the amount of exhaust gas sent to the supercharger 50, and decrease the rotational speed of the supercharger 50. However, since there is a risk that the furnace space rate may become too large compared to the appropriate range for decomposing N2O, in some cases, the compressed air sent to the air preheater 30 in the supply path 56 is adjusted by reducing the opening degree of the excess air regulating valve 49 to maintain the pressure after the supply path 56.

[0058] When S1 < S1min is not satisfied in (S4) (i.e., S1 ≥ S1min), it is determined whether S1max < S1 (S6). If S1max < S1, an operation to increase P1 is carried out (S7). The operation to increase P1 is to decrease the opening degree of the regulating valve 48 in the bypass path 43, increase the amount of exhaust gas sent to the supercharger 50, and increase the rotational speed of the supercharger 50. However, since there is a risk that the furnace space rate may be too low to decompose N2O while the fluidized bed 3 in the fluidized incinerator may not flow sufficiently, leading to incomplete combustion of the incineration target, in some cases, the compressed air sent to the air preheater 30 in the supply path 56 is adjusted by increasing the opening degree of the excess air regulating valve 49 to maintain the pressure after the supply path 56. If S1max < S1 is not satisfied, the process ends as it is (END). By periodically performing the above steps, the pressure within the incineration system 1 using the forced-feed fluidized incinerator can be adjusted, the furnace space rate can be controlled, and the residence time of the gas accompanying the generation of gas within the furnace can be maintained to suppress the generation of N2O.

Explanation of symbols

[0059] 1: Incineration system 2: Fluidized bed incinerator 10: Sludge supply device 15:Water supply device 17: Control valve (CV2) 20: Fuel supply device 22: Control valve (CV1) 23: Thermometer 24: Thermometer 25: Pressure gauge 26: Air preheater air volume measuring instrument 27: Air preheater air volume measuring instrument 28: Turbocharger rotation speed measuring instrument 30: Air preheater 40: Dust collector 47: Control valve (CV3) 48: Control valve (CV4) 49: Control valve (CV5) 50: Turbocharger 60: Start-up blower 70: White smoke prevention fan 75: White smoke preventer 80: Flue gas treatment tower 90: Control device

Claims

1. Nitrogen in exhaust gas for controlling a fluidized bed incinerator that incinerates materials that mainly include sludge ２ 1. A method for reducing O emissions, comprising: Calculate the amount of exhaust gas discharged from the fluidized bed incinerator based on the gas generated in the fluidized bed incinerator, or directly measure the amount of exhaust gas; Calculating the superficial velocity of the fluidized bed incinerator based on the calculated or measured amount of exhaust gas; adjusting the pressure of the compressed air supplied from the turbocharger to control the superficial velocity; In controlling the superficial velocity, the superficial velocity is controlled to a value at which the discrepancy between the correlation equation-calculated N 2 O and the measured N 2 O value is 0 or less. ２ Methods for reducing O emissions.

2. the superficial velocity is compared with a set minimum value, and if the superficial velocity falls below the minimum value, the opening of a control valve in the exhaust gas bypass passage of the turbocharger is increased, the amount of exhaust gas sent to the turbocharger is reduced, the rotation speed of the turbocharger is lowered, and the opening of an excess air control valve is reduced, thereby maintaining the pressure after the supply passage for supplying compressed air from the turbocharger, The superficial velocity is compared with a set maximum value, and if the superficial velocity exceeds the maximum value, the opening of a control valve in the exhaust gas bypass passage of the turbocharger is reduced, the amount of exhaust gas sent to the turbocharger is increased, the rotation speed of the turbocharger is increased, and the opening of the excess air control valve is increased, so as to maintain the pressure after the supply passage. ２ Methods for reducing O emissions.

3. A control device for controlling a fluidized bed incinerator that incinerates materials to be incinerated, the main incineration target being sludge, Calculate the amount of exhaust gas discharged from the fluidized bed incinerator based on the gas generated in the fluidized bed incinerator, or directly measure the amount of exhaust gas; Calculating the superficial velocity of the fluidized bed incinerator based on the calculated or measured amount of exhaust gas; The pressure of the compressed air supplied from the turbocharger is adjusted to control the superficial velocity of the N2 in the exhaust gas. ２ Operates based on a control program that executes O emission reduction; The control device controls the superficial velocity so that the deviation between the correlation equation-calculated N 2 O and the measured N 2 O value is 0 or less.

4. the superficial velocity is compared with a set minimum value, and if the superficial velocity falls below the minimum value, the opening of a control valve in the exhaust gas bypass passage of the turbocharger is increased, the amount of exhaust gas sent to the turbocharger is reduced, the rotation speed of the turbocharger is lowered, and the opening of an excess air control valve is reduced, thereby maintaining the pressure after the supply passage for supplying compressed air from the turbocharger, 4. The control device according to claim 3, wherein the superficial velocity is compared with a set maximum value, and if the superficial velocity exceeds the maximum value, the aperture of a control valve in the exhaust gas bypass passage of the turbocharger is reduced to increase the amount of exhaust gas sent to the turbocharger, thereby increasing the rotation speed of the turbocharger, and the aperture of a surplus air control valve is increased to maintain the pressure after the supply passage.

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