Method and device for reducing N2O emissions in exhaust gases

Abstract

To provide a control method and a control device for reducing a discharge amount of N2O in adjustment of a combustion residence time in a fluidized incinerator to realize an operation index in the fluidized incinerator, without increasing a temperature in the incinerator under a condition of an in-furnace set temperature necessary for decomposition of N2O.SOLUTION: An in-furnace residence time is also applied as an index in reduction of N2O, by focusing the in-furnace residence time of an incineration exhaust gas, in addition to a temperature condition.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 the 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, or fluidizing 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.

[0003] 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. 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).

[0004] To reduce exhaust gases, particularly emissions of 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).

[0005] For example, in a turbocharged fluidized bed sludge incinerator, combustion begins in the furnace bed and is carried out at a temperature of 870-880°C from the furnace top to the furnace outlet, thereby decomposing N2O (the greenhouse effect of N2O is 298 times that of carbon dioxide equivalent). 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 when the dewatered sludge has low moisture content and is easy to burn, and cooling by injecting water into the furnace when the temperature inside the furnace rises (spontaneous combustion state). [Prior art documents] [Patent documents]

[0006] [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 Summary of the Invention [Problem to be solved by the invention]

[0007] 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 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.

[0008] 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.

[0009] 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 material to be incinerated, the combustion of auxiliary fuel, and the injection of water into the incinerator. For this reason, it is difficult to accurately represent the flow state inside the furnace using, for example, the superficial velocity determined using only the amount of air supplied.

[0010] 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.

[0011] 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.

[0012] Figure 2 is a diagram explaining 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 2, N2O decomposition is correlated with furnace temperature.

[0013] 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 2. Therefore, it becomes difficult to meet the demand for reduced N2O emissions simply by increasing the furnace temperature.

[0014] Even if it is possible to accelerate the decomposition of NO by further increasing the temperature inside the furnace, there is a high possibility of adverse effects due to the generation of more localized high temperature areas, and adverse effects 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.

[0015] The object of the present invention is to provide a method and apparatus for operating a fluidized bed incinerator that does not increase costs by improving the heat resistance of the incineration equipment while maintaining the incineration temperature required for NO decomposition, and more specifically, to provide a method and apparatus for reducing NO emissions that achieves an operating index for adjusting the gas residence time in the fluidized bed incinerator. [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 flue gas space rate (superficial velocity) in the incinerator. The space rate is calculated by calculating the gas generation rate from the fluidized bed 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 bed incinerator 2. The flue gas generation rate from the fluidized bed incinerator 2 can be measured directly. However, if measurement is difficult due to the influence of ash in the flue gas, the flue gas volume can be measured downstream from the outlet of the dust collector 40 (e.g., supply line 41). When calculating the space rate from the supply amounts indicated by each measuring device, first calculate the mass flow rate from each supply amount, convert it to a volumetric flow rate to determine the gas generation rate, and then calculate the space rate. The gas generation rate for an object to be incinerated is calculated, for example, based on the moisture content, organic component rate, and elemental composition measured by a measuring device or analytical work. It is acceptable to calculate the gas generation rate for an object to be incinerated using values ​​obtained by statistically organizing values ​​obtained by daily measuring devices or analytical work, rather than using real-time measurements.

[0019] However, because option (1) above leads to increased equipment costs, option (2) is usually used. Increasing the furnace pressure is an effective way to reduce the exhaust gas space rate inside the furnace, assuming a constant mass flow rate. However, increasing the pressure increases the pressure required to send combustion air into the furnace, which increases the air density, promoting heat exchange in the air preheater and raising the furnace inlet air temperature (T2). This has no effect when auxiliary fuel is used to control the furnace bed temperature T1, but when temperature control is performed by injecting water into the furnace, the increase in furnace inlet air temperature T2 increases the amount of water injected, which increases the exhaust gas flow rate. As a result, the furnace space rate increases.

[0020] 1, when adjusting the distribution of supply air through the branch line composed of supply line 56 (composed of branch supply lines 56a and 56b) and control valve 47, branch supply line 56a (parallel flow line) reduces the heat exchange area between the exhaust gas and supply air in the air preheater, thereby reducing the heat exchange rate, while branch supply line 56b (counterflow line) increases the heat exchange area between the exhaust gas and supply air in the air preheater, thereby increasing the heat exchange rate. By increasing the proportion of supply air passing through the parallel flow line, and lowering the furnace inlet air temperature T2, the increase in hearth temperature T1 is suppressed, which in turn suppresses the increase in the amount of water injected into the furnace and the increase in the furnace space rate. This results in reduced NO emissions.

[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 2. 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 method is disclosed in Patent Document 4, but the present invention is characterized in that it is a method and apparatus for reducing NO by applying the technology of "adjusting the temperature of preheated air (combustion air) by operating pressure" described in the above paragraph

[0020] and "fluctuation of the heat exchange (parallel flow / counter flow) bias ratio of the air preheater, and temperature adjustment" described in the above paragraph

[0021] to manage and adjust the space rate for the purpose of the residence time of gas in the furnace at high temperatures 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] Then, (c): The operations in (a) and (b) increase the heat transfer rate of the air preheater, raising the air temperature inside the furnace. If the temperature inside the furnace is too high, the amount of water injected will increase, shortening the gas residence time in the high-temperature furnace area and increasing NO2O. In this case, in the countercurrent and parallel current lines that branch the supply air to the air preheater, the ratio of air flowing through the countercurrent and parallel current lines is adjusted using control valve 47 on the countercurrent line side, changing the heat transfer rate of the air preheater. When it is desired to lower the temperature, the amount of water injected into the parallel current line is increased, and by lowering the preheated air temperature, the temperature inside the furnace is lowered, the amount of water injected into the furnace is reduced, and the space rate inside the furnace is suppressed, thereby reducing NO2O emissions.

[0026] 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.

[0027] The methods for reducing N2O emissions in exhaust gas from fluidized bed incinerators that incinerate materials, primarily sludge, are as follows:

[0028] (1) A method for reducing NO emissions in exhaust gas for controlling a fluidized bed incinerator that incinerates materials to be incinerated, the main incineration target being sludge, comprising: The aforementioned The amount of exhaust gas emitted from the fluidized bed incinerator detection death, detectionThe superficial velocity of the fluidized bed incinerator is calculated based on the amount of exhaust gas thus calculated, and when the superficial velocity falls below a target lower limit, the pressure of the compressed air supplied from the turbocharger is reduced, and when the superficial velocity exceeds a target upper limit, the pressure of the compressed air supplied from the turbocharger is increased. In addition, if the amount of water injected into the furnace exceeds the upper limit of the target value, the furnace inlet air temperature is lowered, and if the amount of water injected into the furnace falls below the lower limit of the target value, the furnace inlet air temperature is raised. It is characterized by:

[0030] ( 2 ) A method for reducing NO emissions in exhaust gas for controlling a fluidized bed incinerator that incinerates materials to be incinerated, the main incineration target being sludge, comprising: controlling the amount of a plurality of feed materials to be supplied to the fluidized bed incinerator, the feed materials being the materials to be incinerated, water, fuel, and air; Weigh the result The method is characterized in that the amount of exhaust gas discharged from the fluidized bed incinerator is calculated based on the above, or the amount of exhaust gas is directly measured (hereinafter, both are referred to as "detection"), and the superficial velocity of the fluidized bed incinerator is calculated based on the calculated or measured amount of exhaust gas.

[0031] ( 3 ) the superficial velocity Lower target value Compared with the superficial velocity Lower target value If the exhaust gas amount falls below 100%, the opening of the 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 reduced, and the opening of the excess air control valve is reduced. Compressed air is supplied from the turbocharger The pressure after the supply line is maintained, and the superficial velocity is Target upper limit Compared with the superficial velocity Target upper limit If the pressure exceeds the specified value, the opening of the 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 surplus air control valve is increased, thereby maintaining the pressure after the supply passage.

[0032] ( 4 ) If the amount of water injected into the reactor exceeds the upper limit of the target value, supply route Compressed air sent through Branching By reducing the opening of the branch control valve, the compressed air in the parallel flow line is increased to reduce the heat exchange in the air preheater, and the furnace inlet air temperature is lowered. If the amount of water injected into the furnace falls below the target lower limit, The aforementioned By increasing the opening of the branch control valve, the amount of compressed air in the counterflow line is increased to increase the heat exchange in the air preheater, thereby raising the furnace inlet air temperature.

[0033] In addition, the equipment for reducing N2O emissions in exhaust gas is as described below.

[0034] ( 5 ) A device for reducing NO emissions in exhaust gas for controlling a fluidized bed incinerator that incinerates materials to be incinerated, the main incineration target of which is sludge, The aforementioned The amount of exhaust gas emitted from the fluidized bed incinerator detection do Exhaust gas volume detection Means and detection The superficial velocity of the fluidized bed incinerator is calculated based on the amount of exhaust gas. A superficial velocity calculation means When the superficial velocity falls below a target lower limit, the pressure of the compressed air supplied from the turbocharger is reduced, and when the superficial velocity exceeds a target upper limit, the pressure of the compressed air supplied from the turbocharger is increased. Compressed air pressure adjustment means and a furnace inlet air temperature adjusting means for lowering the furnace inlet air temperature when the amount of water poured into the furnace exceeds an upper limit of a target value, and for raising the furnace inlet air temperature when the amount of water poured into the furnace falls below a lower limit of a target value. The present invention is characterized by the following.

[0036] ( 6 ) A device for reducing N2O emissions in exhaust gas for controlling a fluidized bed incinerator that incinerates materials to be incinerated, with sludge as the main incineration target. 、 Detecting the amount of exhaust gas emitted from the fluidized bed incinerator have the means to , When the means for detecting the amount of exhaust gas calculates the amount of exhaust gas based on the supply amounts of a plurality of supplies consisting of the material to be incinerated, water, fuel, and air, which are supplies supplied to the fluidized bed incinerator, of The apparatus further includes a supply measuring means for measuring the amount of exhaust gas, and the means for detecting the amount of exhaust gas calculates the amount of exhaust gas based on the measurement result of the supply measuring means. It is characterized by:

[0037] ( 7 ) An apparatus for reducing NO emissions in exhaust gas for controlling a fluidized bed incinerator that incinerates materials to be incinerated, the main incineration target being sludge, wherein the superficial velocity is Lower target value Compared with the superficial velocity Lower target value If the exhaust gas amount falls below 100%, the opening of the 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 reduced, and the opening of the excess air control valve is reduced. Compressed air is supplied from the turbocharger The pressure after the supply line is maintained, and the superficial velocity is Target upper limit Compared with the superficial velocity Target upper limit If the pressure exceeds the specified 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 number of revolutions of the turbocharger is increased, and the opening of the surplus air control valve is increased, thereby maintaining the pressure after the supply passage.

[0038] ( 8 ) A device for reducing N2O emissions in exhaust gas for controlling a fluidized bed incinerator that incinerates materials to be incinerated, the main incineration target being sludge, and if the amount of water injected into the furnace exceeds the target upper limit, supply route Compressed air sent through Branching By reducing the opening of the branch control valve, the amount of compressed air in the parallel flow line can be increased to reduce the heat exchange in the air preheater, and the furnace inlet air temperature can be lowered. If the amount of water injected into the furnace falls below the target lower limit, , the above The system is characterized by being equipped with a means for increasing the opening of the branch control valve to increase the amount of compressed air in the counterflow line so as to increase the heat exchange in the air preheater, thereby raising the furnace inlet air temperature.

[0039] The present invention is not limited to the above configurations or the configurations described in the embodiments below, and it goes without saying that various modifications are possible without departing from the technical concept of the present invention. [Effects of the Invention]

[0040] According to the present invention, in order to maintain the incineration temperature required for NO decomposition, the heat resistance of the fluidized bed incineration equipment can be improved, thereby ensuring the amount of NO emissions without increasing costs, and achieving the following effects.

[0041] (1) 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 solid content. Dewatered sludge with low moisture content and a high solid content has a high calorific value and is therefore prone to spontaneous combustion. During spontaneous combustion, 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 reduces the decomposition of N2O, 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.

[0042] (2) However, as described in paragraph

[0020] , if the heat exchange efficiency of the air preheater increases, the furnace inlet air temperature rises, and the furnace temperature reaches the point where water is again injected into the furnace, the amount of gas generated in the furnace increases due to the influence of water injection into the furnace, shortening the gas residence time. To prevent the increase in the furnace inlet air temperature, a separate air cooler could be installed to intake air with a fan and exchange heat with the supply air, but this would increase the amount of equipment required. Therefore, without making major changes to the current equipment, as described in paragraph

[0021] , the heat exchange (parallel / counterflow) bias ratio of the air preheater can be adjusted using a damper. This reduces the heat exchange efficiency and the combustion air temperature, thereby lowering the furnace temperature, reducing the amount of water injection and the amount of gas generated. This maintains the space rate and ensures gas residence time in the high-temperature furnace, thereby maintaining NO decomposition. [Brief explanation of the drawings]

[0043] [Figure 1] System configuration diagram illustrating an example of a control device for reducing N2O emissions in adjusting combustion residence time in a fluidized incinerator according to the present invention. [Figure 2] Diagram showing an example of the correlation between maximum furnace temperature and N2O emission factor [Figure 3] Illustrative diagram of the discrepancy between furnace space rate and correlation-calculated N2O and measured N2O values [Figure 4] Illustrative diagram of the relationship between the amount of heat in the exhaust gas and the amount of heat exchanged by the air preheater [Figure 5]A flowchart illustrating the N2O emission reduction process executed by the control device. DETAILED DESCRIPTION OF THE INVENTION

[0044] An embodiment of an incinerator system to which the present invention is applied will be described in detail below with reference to FIG.

[0045] Figure 1 is a system configuration diagram illustrating an example of a control device for reducing N2O emissions when adjusting gas residence time in a fluidized incinerator according to the present invention. In Figure 1, this system comprises a fluidized 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. A white smoke prevention device and a flue gas treatment tower are installed downstream of the turbocharger 50, but are not shown in the figure.

[0046] The incineration system 1 also has a thermometer (T) 23, a thermometer (T) 24, a pressure gauge (P) 25, an air preheater cooling air volume measuring instrument (F) 26, an air preheater cooling air volume measuring instrument (F) 27, and a turbocharger rotation speed measuring instrument (R) 28. The incineration system 1 is also provided with a thermometer (T) 81, a supply sludge volume measuring instrument (F) 82, a supply water volume measuring instrument (F) 83, and a supply fuel volume measuring instrument (F) 84.

[0047] The fluidized incinerator 2 described in one embodiment of the present invention is a turbocharged fluidized incinerator. The fluidized incinerator 2 supplies heated compressed air to the incinerator 2 and burns the materials to be incinerated inside the incinerator 2 under high temperature and pressure conditions, thereby increasing the combustion rate and reducing emissions of harmful substances such as NO. In the following description, the fluidized incinerator 2 will also be simply referred to as the incinerator 2.

[0048] In FIG. 1, thick solid lines with arrows indicate supply paths (supply pipes) for sludge (cake), auxiliary fuel, air, water, or exhaust gas, and dashed lines with arrows indicate bypass paths. The thin solid lines with arrows ((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 cooling air amount measuring device 27, (4) a line connecting the air preheater cooling 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), and (8) a line connecting the air preheater cooling air amount measuring device 26 to the control valve 47 (CV3)) are signal lines that send control signals, etc. from the control device 9 to these devices, for example.

[0049] The measurement signals from each measuring instrument and the control signals to each control valve are input to the control device and sent to the corresponding control valve 49 after predetermined calculation processing, but in FIG. 1, most of the signal connection lines to the control device 90 have been omitted for ease of understanding. Also, (1) the line connected from the pressure gauge 25 to the control valve 48 (CV4) indicates a control signal line that is connected to the control valve 48 (CV4) for transmitting a pressure value signal to adjust the opening degree thereof.

[0050] The fluidized bed incinerator 2 is equipped with a fluidized bed 3, a preheated air intake 4, and a startup burner 5. It also has a sludge inlet (not shown) that takes in sludge supplied via a valve 19 from a supply channel (sludge supply pipe) 11 connected to a sludge (cake) supply device 10, a water (water injection) inlet (not shown) that takes in water (water injection) supplied from a supply channel (water supply pipe) 16 connected to a water supply device 15, and a fuel inlet (not shown) that takes in auxiliary fuel supplied from a supply channel (fuel supply pipe) 21 connected to a fuel supply device 20.

[0051] The sludge (cake) supplying device 10 sequentially supplies sewage sludge cakes, which have been sent from a sewage treatment facility (not shown) and stored in a hopper (not shown), from a supply pipe 11 to the incinerator 2 .

[0052] The water supply device 15 adjusts the combustion temperature inside the incinerator 2 by sending water (injected water) into the incinerator 2 from a connected supply pipe 16. The fuel supply device 20 adjusts the combustion temperature inside the incinerator 2 by sending auxiliary fuel from a connected supply pipe 21 into the incinerator 2.

[0053] A control valve 17 (CV2) is provided in the water supply pipe 16, and a control valve 22 (CV1) is provided in the fuel supply pipe 21. The control valves 17 (CV2) and 22 (CV1) are connected to a control device 90, and their openings are adjusted in response to control signals output from the control device 90.

[0054] The thermometer (T) 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.

[0055] The thermometer (T) 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.

[0056] The pressure gauge (P) 25 measures the pressure 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.

[0057] The air preheater cooling air amount measuring instrument (F) 26 measures the amount of compressed air supplied from the turbocharger 50 to the air preheater 30. The air preheater cooling 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.

[0058] The air preheater air amount measuring instrument (F) 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.

[0059] The rotation speed measuring device (R) 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.

[0060] In the air preheater 30, heat is exchanged between the exhaust gas sent from the fluidized bed incinerator 2 via the supply line 58 and the compressed air sent from the turbocharger 50 via the supply line 56, the branch supply lines 56a and 56b. The air that has undergone heat exchange is then supplied to the incinerator 2 from the preheated air intake 4 via the supply line 29.

[0061] 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 through the supply path 42 to the white smoke prevention preheater.

[0062] 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 to the turbocharger 50 from the dust collector 40 via the supply path 41 and rotates at high speed, thereby rotating the compressor 53 at high speed. The compressor 53 compresses the air taken into the turbocharger 50 and sends the compressed air to the air preheater 30 via the supply path 56, branch supply paths 56a and 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.

[0063] A control valve 47 (CV3) is provided between the branch supply path 56a and the branch supply path 56b in the supply path 56. 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 the air to the upper side of the air preheater 30 and the branch supply passage 56b supplying the air to the lower side of the air preheater 30 is adjusted.

[0064] When the incineration system 1 is started up, the startup blower 60 supplies the air it has taken in 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.

[0065] 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 to supply atmospheric air from the supply path 65 to the turbocharger 50. Reference numeral 66 denotes a control valve provided in the supply path 65, which is connected to the control device 90 and has its opening adjusted in response to a control signal output from the control device 90.

[0066] The white smoke prevention fan 70 sends the air it takes in to a white smoke prevention device (not shown). The white smoke prevention device heats the air sent in from the white smoke prevention fan 70, which takes in atmospheric air, by exchanging heat with the exhaust gas discharged from the turbocharger 50, which is supplied via a supply path 42. The heated air is sent to a flue gas treatment tower (not shown). The flue gas treatment tower removes air pollutants such as sulfur oxides and soot contained in the exhaust gas from the exhaust gas.

[0067] A supercharger exhaust gas bypass control valve 48 (CV4) is provided in a bypass passage 43 provided between the supply passage 41 and the supply passage 42. The supercharger exhaust gas bypass control valve 48 (CV4) is connected to a control device 90, and its opening is adjusted in response to a control signal output from the control device 90. The amount of exhaust gas sent from the supply passage 41 to the turbocharger 50 is adjusted by adjusting this opening. When the opening of the turbocharger exhaust gas bypass control valve 48 (CV4) is increased, the amount of exhaust gas sent to the turbocharger 50 decreases.

[0068] The pressure in the compressed air supply path after the compressor 53, the air preheater 30, and the incinerator 2 is adjusted according to the amount of exhaust gas sent from the supply path 41 to the turbocharger 50. In addition, a bypass path 57 provided between the air supply path 56 and the supply path 71 is provided with a surplus air control valve 49 (CV5).

[0069] The surplus air control valve 49 (CV5) 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 sent from the turbocharger 50 to the supply path 56 is adjusted. For example, if the opening of the surplus air control valve 49 (CV5) is increased, the amount of exhaust gas sent from the bypass path 57 to the supply path 71 increases, and the amount of compressed air sent from the supply path 56 to the air preheater 30 decreases. The amount of compressed air sent from the supply path 56 to the air preheater 30 is then adjusted.

[0070] 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 has data processing functions such as ROM, RAM memory, a data storage unit, an input / output unit, and the like, as well as a first calculation unit (gas amount calculation unit) 91 and a second calculation unit (space rate calculation unit) 92 that characterize the present invention.

[0071] 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.

[0072] Figure 3 is a diagram illustrating the deviation [%] between the calculated N2O obtained from the correlation equation in Figure 2 and the measured N2O value in the exhaust gas measured by an analyzer as a function of the furnace space rate [m / sec]. As shown in Figure 3, the deviation [%] between the correlation equation-calculated N2O and the measured N2O value as a function of the furnace space rate [m / sec] can be approximated by a linear line. At an in-furnace space rate of approximately 0.73 m / sec, the discrepancy disappears, and the calculated N2O from the correlation equation matches the measured N2O. Above this range, the discrepancy increases in the positive direction, with the measured N2O value being greater than the calculated N2O. This indicates that the actual amount of N2O emitted increases due to the shorter gas residence time in the furnace at higher space rates. On the other hand, at in-furnace space rates below 0.73 m / sec, the discrepancy increases in the negative direction, with the measured N2O value being smaller than the calculated N2O. This indicates that the actual amount of N2O emitted decreases due to the longer gas residence time in the furnace at lower space rates. This suggests that N2O emissions can be reduced by minimizing the in-furnace space rate [m / sec] as much as possible.

[0073] Figure 4 illustrates the relationship between the heat output of the exhaust gas and the heat output of the air preheater, as explained in section (2) of the Effects of the Invention. The upper curve shows the heat output of the air preheater when the cooling air ratio in the parallel flow line is 20%, while the lower curve shows the heat output of the air preheater when the cooling air ratio in the parallel flow line is 40%. The horizontal axis shows the heat output of the exhaust gas converted to the amount of air supplied to the fluidized-bed incinerator. By adjusting the bias ratio, which changes the ratio of air supplied to the incinerator between parallel and counterflow lines, for example, if the incinerator temperature rises and is difficult to lower even when water is being injected into the incinerator, increasing the air ratio in the parallel flow line reduces the heat output of the air preheater, lowering the supply air temperature and maintaining the incinerator temperature at an appropriate combustion temperature. By providing a means for lowering the temperature of the air supplied to the furnace in addition to the water injection means, it is possible to reliably maintain the temperature inside the furnace at an appropriate combustion temperature, suppress an increase in exhaust gas due to water injection into the furnace, optimize the space rate inside the furnace, and ensure the residence time of gas generated in the furnace, thereby maintaining appropriate NO decomposition.

[0074] 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.

[0075] 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 denoted as S-1).

[0076] Next, the exhaust gas volume flow rate is calculated from the furnace temperature T3 and the furnace pressure P1 (S-2), and then the furnace space rate S1 is calculated (S-3).

[0077] The furnace space rate S1 is compared with the set minimum value S1min (S-4). If S1 < S1min, an operation to lower P1 is executed (S-5). The operation to lower P1 is to increase the opening degree of the control valve 48 in the bypass passage 43 and reduce the amount of exhaust gas sent to the supercharger 50 to lower the rotational speed of the supercharger 50. However, since there is a risk that the furnace space rate will 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 passage 56 is adjusted by reducing the opening degree of the excess air control valve 49 to maintain the pressure after the supply passage 56.

[0078] When S1 < S1min is not true in (S-4) (when S1 ≥ S1min), it is determined whether S1max < S1 (S-6). If S1max < S1, an operation to increase P1 is carried out (S-7). The operation to increase P1 is to reduce the opening degree of the control valve 48 in the bypass passage 43 and increase the amount of exhaust gas sent to the supercharger 50 to increase the rotational speed of the supercharger 50. However, since there is a risk that the furnace space rate is too low to decompose N2O while the fluidized bed 3 in the fluidized incinerator cannot 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 passage 56 is adjusted by increasing the opening degree of the excess air control valve 49 to maintain the pressure after the supply passage 56. When S1max < S1 is not true (when S1min ≤ S1 ≤ S1max), the process ends as it is (END).

[0079] On one hand, in response to the start (START) of the process, it is determined whether F4max < F4 (S-8). If F4max < F4, an operation to lower T2 is executed (S-9). The operation to lower T2 means that the compressed air sent from the supercharger 50 through the supply path 56 branches into the supply path 56a and the supply path 56b. By reducing the opening degree of the regulating valve 47, the amount of compressed air passing through the supply path 56a is increased, that is, the compressed air in the parallel flow line is increased so that the heat exchange in the air preheater 30 can be reduced, and an example is to lower the furnace inlet air temperature T2 of the supply air to the fluidized incinerator 2. If it is determined in (S-8) that F4max < F4 is not true, F4min>F4 it is determined whether it is (S-10), F4min>F4 and if so, an operation to raise T2 is executed (S-11). The operation to raise T2 means that the compressed air sent from the supercharger 50 through the supply path 56 branches into the supply path 56a and the supply path 56b. By increasing the opening degree of the regulating valve 47, the amount of compressed air passing through the supply path 56b is increased, that is, the compressed air in the countercurrent line is increased so that the heat exchange in the air preheater 30 can be increased, and an example is to raise the furnace inlet air temperature T2 of the supply air to the fluidized incinerator 2. F4min>F4 If not, the operation is terminated (END).

[0080] By repeatedly executing the above operation at a predetermined cycle, the amount of N2O in the exhaust gas can be reduced.

Explanation of Signs

[0081] 1: Incineration system 2: Fluidized incinerator 3: Fluidized bed 4: Preheated air intake 5: Starting burner 10: Sludge supply device 11: Sludge supply path 15: Water supply device 16: Water supply path 17: Regulating valve (CV2: Water supply amount) 19: Valve 20: Fuel supply device 21: Fuel supply path 22: Control valve (CV1: fuel supply amount) 23: Thermometer (T:T1 measurement) 24: Thermometer (T:T2 measurement) 25: Pressure gauge (P: P1 measurement) 26: Air preheater cooling air volume measuring instrument (F:F1 measurement) 27: Air preheater cooling air volume measuring instrument (F:F2 measurement) 28: Rotation speed measuring device (R: R1 measurement) 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 81: Thermometer (T:T3 measurement) 82: Sludge supply volume measuring instrument (F:F3 measurement) 83: Water supply volume meter (F:F4 measurement) 84: Fuel supply amount meter (F:F5 measurement) 90: Control device (compares each measurement value with the set value / threshold value and calculates the appropriate control value) 91: Gas volume calculation unit 92: Sky tower velocity calculation part

Claims

1. Nitrogen in exhaust gas for controlling a fluidized bed incinerator that incinerates materials that mainly include sludge 2 A method for reducing O emissions, comprising: Detecting the amount of exhaust gas discharged from the fluidized bed incinerator; Calculating the superficial velocity of the fluidized bed incinerator based on the detected amount of exhaust gas; In addition to reducing the pressure of the compressed air supplied from the turbocharger when the superficial velocity falls below a target lower limit, and increasing the pressure of the compressed air supplied from the turbocharger when the superficial velocity exceeds a target upper limit, If the amount of water injected into the furnace exceeds the upper limit of the target value, the furnace inlet air temperature is lowered, and if the amount of water injected into the furnace falls below the lower limit of the target value, the furnace inlet air temperature is raised. N in exhaust gas characterized by 2 Methods for reducing O emissions.

2. The amount of exhaust gas is detected by measuring the amount of a plurality of supplies, which are the materials to be incinerated, water, fuel, and air, supplied to the fluidized incinerator, and calculating the amount of exhaust gas discharged from the fluidized incinerator based on the measurement results, or by directly measuring the amount of exhaust gas; 2. The method according to claim 1, wherein the superficial velocity of the fluidized bed incinerator is calculated based on the detected amount of exhaust gas. 2 Methods for reducing O emissions.

3. the superficial velocity is compared with a target lower limit, and when the superficial velocity falls below the target lower limit, the aperture 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 aperture of an excess air control valve is reduced, thereby maintaining the pressure subsequent to the supply passage for supplying compressed air from the turbocharger, The superficial velocity is compared with an upper limit of a target value, and when the superficial velocity exceeds the upper limit of the target 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 an excess air control valve is increased, so as to maintain the pressure after the supply passage. 2 Methods for reducing O emissions.

4. When the amount of water injected into the furnace exceeds an upper limit of a target value, the opening of a branch control valve that branches the compressed air sent from the turbocharger through a supply line is reduced, thereby increasing the amount of compressed air in the parallel flow line so as to reduce heat exchange in the air preheater, thereby lowering the furnace inlet air temperature; When the amount of water injected into the furnace falls below a target lower limit, the opening of the branch control valve that branches the compressed air sent from the turbocharger through the supply line is increased, thereby increasing the amount of compressed air in the counterflow line so as to increase heat exchange in the air preheater, thereby raising the furnace inlet air temperature. 2 Methods for reducing O emissions.

5. Nitrogen in exhaust gas for controlling a fluidized bed incinerator that incinerates materials that mainly include sludge 2 An apparatus for reducing O emissions, comprising: an exhaust gas amount detection means for detecting the amount of exhaust gas discharged from the fluidized bed incinerator; a superficial velocity calculation means for calculating the superficial velocity of the fluidized bed incinerator based on the amount of exhaust gas detected by the exhaust gas amount detection means; a compressed air pressure adjusting means for reducing the pressure of the compressed air supplied from the turbocharger when the superficial velocity falls below a target lower limit, and for increasing the pressure of the compressed air supplied from the turbocharger when the superficial velocity exceeds a target upper limit; a furnace inlet air temperature adjusting means for lowering the furnace inlet air temperature when the amount of water poured into the furnace exceeds an upper limit of a target value, and for raising the furnace inlet air temperature when the amount of water poured into the furnace falls below a lower limit of a target value; N in exhaust gas, characterized by comprising 2 A device that reduces O emissions.

6. The exhaust gas amount detection means comprises at least one of an exhaust gas amount calculation means for calculating the amount of exhaust gas discharged from the fluidized bed incinerator, or a means for directly measuring the amount of exhaust gas; When the flue gas amount calculation means is provided, the incinerator further includes a feed material metering means for metering the amount of a plurality of feed materials, which are the materials to be incinerated, water, fuel, and air, supplied to the fluidized bed incinerator, and the flue gas amount calculation means calculates the amount of flue gas based on the measurement results of the feed material metering means. The nitrogen in the exhaust gas according to claim 5, 2 A device that reduces O emissions.

7. an excess air control valve that compares the superficial velocity with a target lower limit, and when the superficial velocity falls below the target lower limit, increases the opening of a valve in the exhaust gas bypass passage of the turbocharger, reduces the amount of exhaust gas sent to the turbocharger, lowers the rotation speed of the turbocharger, and reduces the opening of the valve to maintain the pressure after the supply passage that supplies compressed air from the turbocharger; and an opening adjustment valve provided midway through the exhaust gas bypass path that compares the superficial velocity with a target upper limit, and operates to reduce an opening of a valve midway through the exhaust gas bypass path of the turbocharger when the superficial velocity exceeds the target upper limit; 7. The method according to claim 5, wherein the amount of exhaust gas sent to the turbocharger is increased to increase the rotational speed of the turbocharger and the opening of the excess air control valve is increased to maintain the pressure after the supply line. 2 A device that reduces O emissions.

8. a branch adjustment valve that branches the compressed air supplied from the turbocharger through a supply passage, When the amount of water injected into the furnace exceeds an upper limit of a target value, the compressed air that is branched by the branch adjustment valve and sent from the turbocharger through the supply path is increased by reducing the opening of the branch adjustment valve, thereby increasing the amount of compressed air in the parallel flow line so as to reduce heat exchange in the air preheater, thereby lowering the furnace inlet air temperature; When the amount of water injected into the furnace falls below the target lower limit, the opening of the branch control valve is increased for the branched compressed air sent from the turbocharger through the supply line, thereby increasing the amount of compressed air in the counterflow line so as to increase heat exchange in the air preheater, thereby raising the furnace inlet air temperature. 2 A device that reduces O emissions.

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