JP2023151263A - Method and device for reducing discharge amount of n2o in exhaust gas - Google Patents

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

The present invention relates to the control of a fluidized incinerator that controls the flow state of a fluidized medium such as sludge flowing in the incinerator, and in particular, the present invention relates to the control of a fluidized incinerator that controls the fluidization state of a fluidized medium such as sludge, and in particular, N ₂ O, which is a greenhouse gas, is used in adjusting the residence time of combustion gas in the fluidized incinerator. This invention relates to a method and device for reducing emissions.

A fluidized incinerator generates a fluidized bed by fluidizing a fluidized medium such as sand placed in the furnace using air sent from the bottom of the furnace. This is an incinerator that incinerates objects to be incinerated, such as garbage, by stirring them together with a fluid medium. The fluid state in a fluidized bed incinerator depends on the air supplied to the furnace (also simply referred to as supply air, combustion air, or fluidized air), the amount of materials to be incinerated, auxiliary fuel, etc., and the temperature and pressure inside the furnace. It is important to optimize the combustion state by stabilizing the fluid state and increasing the combustion efficiency of the material to be incinerated.

Additionally, in order to prevent global warming, it is necessary to reduce the emissions of N ₂ O (nitrous oxide), which is a greenhouse gas generated from exhaust gas when incinerating organic components contained in materials to be incinerated. There is.
For example, in a fluidized fluid incinerator, the amount of air supplied to the furnace to make the fluidized medium flow is adjusted depending on the brightness inside the furnace, the amount of material to be incinerated, the temperature, the oxygen concentration, or the pressure inside the furnace. A method has been proposed (see Patent Document 1).
In addition, in a fluidized bed incinerator, the increase or decrease in the moisture content of the sewage sludge cake is estimated based on the oxygen concentration of the exhaust gas and the moisture concentration in the upper part of the furnace, and based on the estimation results, the amount of air supplied to the furnace, A method has been proposed for stabilizing combustion by adjusting the temperature, the amount of materials to be incinerated supplied to the furnace, etc. (see Patent Document 2).

Regarding the reduction of exhaust gas emissions, particularly N ₂ O and NOx, a method is known in which a slurry-like mixture of an ammonia-based reducing agent and a porous fluidizing medium is injected into a furnace (see Patent Document 3).

For example, in a supercharged fluidized bed sludge incinerator, N ₂ O is decomposed by combustion that starts at the hearth _and continues from the top of the furnace to the furnace exit at a temperature of 870 to 880°C. is 298 times the amount of carbon dioxide equivalent).
The temperature of the incinerator is controlled by supplying auxiliary fuel for combustion (assisted combustion state), or not supplying auxiliary fuel if the dehydrated sludge has low water content and is easily combustible, in order to maintain the temperature inside the furnace depending on the properties of the dehydrated sludge. The temperature is controlled by combustion (self-combustion state), which cools down the furnace by injecting water when the temperature inside the furnace rises.

Patent No. 3108742 Japanese Patent Application Publication No. 2004-125332 Patent No. 5640120 Japanese Patent Application Publication No. 2020-159655

In this type of fluidized incinerator, superficial velocity is one of the indicators indicating the fluid state within the incinerator. For example, when designing a fluidized bed incinerator, a superficial velocity suitable for operation at a given load is set, and the size and flow rate of the incinerator are set so that the material to be incinerated is incinerated at the set superficial velocity. The particle size etc. of the medium are determined. Since the flow state within the furnace is correlated with the superficial velocity within the furnace, it is possible to indirectly confirm the flow state if the superficial velocity during operation, which is not the design value, can be determined.
For example, if the superficial velocity falls below the appropriate range and insufficient flow of the fluidized medium occurs, the combustion efficiency will decrease, and the ash generated by combustion will be difficult to discharge from the furnace, causing ash content to be added to the fluidized sand in the furnace. The fluid medium involved will increase.

On the other hand, when the superficial velocity exceeds the appropriate range and the fluidized medium flows excessively, in addition to the ash that is well discharged, the fluidized medium, which is fluidized sand, is scattered outside the furnace, reducing the amount of fluidized medium inside the furnace. Put it away. Withdrawing increased fluidized media from the furnace and replenishing the furnace with decreased fluidized media increases the operating costs of fluidized incinerators. Therefore, it is desirable to operate the fluidized incinerator so that the superficial velocity falls within an appropriate range.

However, the superficial velocity in the incinerator varies depending not only on the amount of air supplied to the incinerator, but also on the amount of gas generated by combustion of the object to be incinerated, auxiliary fuel, and water injection into the incinerator.
For this reason, for example, it is difficult to accurately represent the flow state in the furnace using the superficial velocity determined using only the air supply amount.

In Patent Document 1, a controllable superficial velocity range is set based on the results of each element control at the time of design, but as mentioned above, actual superficial velocity measurement is difficult and has not been implemented.

Furthermore, in order to reduce the amount of N ₂ O discharged from exhaust gases, N ₂ O is decomposed at high temperatures. In the embodiments described below, reduction in the amount of N ₂ O emissions will be explained as an example.

Figure 2 is a diagram illustrating _{an example of the correlation between the maximum temperature inside the furnace and the N 2 O} emission coefficient. -N ₂ O/t-DS] to approximate the correlation formula. As shown in FIG. 2, the decomposition of N ₂ O is correlated with the furnace temperature.

However, when the temperature is increased to further decompose N ₂ O, the amount of N ₂ O reduction decreases, as is clear from the approximate curve in FIG. 2 . Therefore, it becomes difficult to meet the demand for reducing the amount of N ₂ O emissions by simply increasing the temperature inside the furnace.

Even if it is possible to accelerate the decomposition of N ₂ O by further increasing the temperature inside the furnace, there will be adverse effects due to the generation of a higher temperature field locally, and the risk of flying due to the increase in the temperature of the exhaust gas flowing into the air preheater and the increase in the temperature at the furnace outlet. There is a high possibility that harmful effects will occur due to the melting and adhesion of ash, increasing the cost of improving the heat resistance of incineration equipment and taking measures to prevent the melting and adhesion of fly ash, and it is necessary to take separate operation management measures for N ₂ O decomposition. There is.

The purpose of the present invention is to provide a method and apparatus for operating a fluidized incinerator that does not increase costs by improving the heat resistance of incineration equipment in order to maintain the incineration temperature necessary for N ₂ O decomposition, and more specifically, to provide a fluidized incinerator and its device. An object of the present invention is to provide a method for reducing N ₂ O emissions and a device for controlling the same, which realizes an operational index for adjusting gas residence time in a furnace.

In order to achieve the above object, the N ₂ O reduction technology according to the present invention focuses on the residence time of gas generated in the furnace in addition to temperature conditions, and uses the residence time in the furnace as an index for N ₂ O reduction. It is characterized by

As mentioned above, it was thought that the suppression of N ₂ O emissions was correlated with the maximum temperature of the exhaust gas in the furnace, but research by the present inventors revealed that there is also a correlation with the residence time of the gas in the furnace. It turns out that there is something. That is, as will be described later, an inversely proportional relationship is revealed in which the amount of N ₂ O discharged is suppressed as the gas residence time in the furnace increases. Note that data suggesting the above-mentioned correlation is also found in FIG. 3 of Patent Document 3.

There are two methods for increasing the gas residence time in the furnace: (1) enlarging the furnace; and (2) decreasing the exhaust gas space rate (superficial velocity) in the furnace. The space rate is determined by the amount of incinerated material such as sludge from the sludge supply device 10 shown in FIG. 83 (process value of F4)], fuel such as heavy oil in the fuel supply device 20 [supplied fuel amount measuring device 84 (process value of F5)], and combustion air to the fluidized incinerator 2 [air preheater air amount Based on each supply amount of the measuring device 27 (process value of F2), the amount of gas generated from inside the fluidized bed incinerator is calculated and determined. The amount of exhaust gas generated from the fluidized incinerator 2 may be measured directly, or if measurement is difficult due to the influence of ash in the exhaust gas, the amount of exhaust gas generated from the fluidized incinerator 2 may be measured by measuring the amount of exhaust gas generated in the downstream exhaust gas path (supply path 41, etc.) after the exit of the dust collector 40. The amount may also be measured. When calculating the space rate from each supply amount indicated by each measuring device, first, the mass flow rate is calculated from each supply amount, and the gas generation amount is calculated by converting it into a volumetric flow rate to calculate the space rate. Regarding the calculation of the amount of gas generated from the object to be incinerated, for example, the amount of gas generated when the object to be incinerated is incinerated is calculated based on the moisture content, organic component rate, and elemental composition determined by a measuring device and analysis work. It is sufficient to calculate the amount of gas generated from the incineration target using not the real-time measured values but the statistically arranged values obtained by measuring devices and analytical work on a daily basis.

However, since (1) above leads to an increase in equipment costs, (2) is usually used. In order to reduce the space rate of exhaust gas in the furnace, it is effective to increase the pressure in the furnace if the mass flow rate is constant. However, when the pressure is increased, the pressure increases in order to send combustion air into the furnace, so heat exchange in the air preheater progresses by the increase in air density, and the furnace inlet air temperature (T2) increases. There is no effect when auxiliary fuel is used to control the hearth temperature T1 as an incinerator, but when the temperature is controlled by injecting water into the incinerator, the amount of water injected increases due to the increase in the inlet air temperature T2. This results in an increase in the exhaust gas flow rate. As a result, the furnace space rate increases.

For this reason, in the air preheater shown in FIG. The branch supply line 56a (parallel flow line) reduces the heat exchange area between exhaust gas and supply air to reduce the amount of heat exchange, and conversely, heat exchange is performed by increasing the heat exchange area between exhaust gas and supply air in the air preheater. By increasing the proportion of supply air that passes through the parallel flow line among the branch supply paths 56b (countercurrent lines) that increase the amount of supply air and lowering the furnace inlet air temperature T2, it is possible to suppress the rise in the hearth temperature T1. The amount of increase in the amount of water injected into the reactor is suppressed, and an increase in the space rate in the reactor can be suppressed. As a result, the amount of N ₂ O emissions can be suppressed.

In this way, N ₂ O is decomposed in proportion to the gas residence time in a high temperature field, in addition to the temperature correlation shown in FIG. 2 described above. In the present invention, N ₂ O 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.

A similar method is disclosed in Patent Document 4, but the present invention utilizes the "operating pressure" described in the above paragraph [0020] to manage and adjust the space rate for the purpose of gas residence time in the high-temperature field furnace during N ₂ O decomposition. By applying the techniques of "adjustment of preheated air (combustion air) temperature by" and "variation of heat exchange (cocurrent/countercurrent) bias ratio of air preheater, temperature adjustment" described in paragraph [0021] above, N ₂ The present invention is characterized by a method and device for reducing O.

In the present invention, (a): For example, in a supercharged fluidized bed furnace that incinerates sludge with a low moisture content, in a self-combustion state, the temperature inside the furnace increases and the amount of water injection increases, and the residence time in the high temperature field inside the furnace increases. As the length becomes shorter, N ₂ O increases, so we increased the pressure with a supercharger to suppress the space rate in the furnace, increasing the residence time and reducing the amount of N ₂ O discharged.

Moreover, (b): In order to maintain the increased pressure, a part of the flowing air is discharged by the control valve 49 shown in FIG. 1 located in the surplus air release path. If the surplus air is not released, the space rate will become too small to the extent that fluidization will be poor in the fluidized bed 3 in the fluidized incinerator, leading to incomplete combustion of the material to be incinerated. It allows air to escape and maintains the increased pressure.

And (c): The amount of heat transferred from the air preheater increases due to the operations in (a) and (b), and the air temperature in the furnace rises. If the temperature in the furnace is too high, the amount of water injected increases, and The gas residence time in the internal high temperature field becomes shorter and N ₂ O increases. In this case, in the countercurrent and parallel flow lines that branch the air supplied to the air preheater, the control valve 47 on the countercurrent line side adjusts the proportion of air flowing into the countercurrent and parallel flow lines, and the air When you want to change the heat transfer amount of the preheater and lower the temperature, you can increase the amount of parallel flow line, lower the preheating air temperature, lower the furnace temperature, reduce the amount of water injected into the furnace, and increase the space rate inside the furnace. This reduces the amount of N ₂ O emissions.

Typical features of the N ₂ O emission reduction control means according to the present invention are listed below. Here, in order to facilitate understanding of the invention, the reference numerals used in the drawings described in the embodiments described later are also written for each structure. It is not limited.

A method for reducing N ₂ O emissions in exhaust gas in a fluidized fluidized incinerator that incinerates sludge as the main incineration target is as follows.

(1) A method for reducing the amount of N ₂ O emissions in exhaust gas for controlling a fluidized fluidized incinerator that incinerates sludge as the main material to be incinerated, the method comprising: a feed supplied to the fluidized fluidized incinerator; Calculate the amount of exhaust gas discharged from the fluidized bed incinerator based on the supply amount of multiple types of supplies consisting of the incineration target, water, fuel, and air, and based on the calculated amount of exhaust gas. The superficial velocity of the fluidized incinerator is calculated, and if the superficial velocity is below the lower limit of the target value, the pressure of the compressed air supplied from the supercharger is lowered, and the superficial velocity is lower than the upper limit of the target value. If it exceeds the limit, the pressure of the compressed air supplied from the supercharger is increased.

(2) A method for reducing N ₂ O emissions in exhaust gas for controlling a fluidized fluidized incinerator that incinerates sludge as the main target for incineration, and in which the amount of water injected into the furnace exceeds the upper limit of the target value. If the amount of water injected into the furnace is below the lower limit of the target value, the furnace inlet air temperature is increased.

(3) A method for reducing the amount of N ₂ O emissions in exhaust gas for controlling a fluidized fluidized incinerator that incinerates sludge as the main material to be incinerated, the method comprising: a feed supplied to the fluidized fluidized incinerator; Calculate the amount of exhaust gas discharged from the fluidized bed incinerator based on the amount of the incineration target, water, fuel, and air, or directly measure the amount of exhaust gas (hereinafter referred to as Both of these are referred to as "detection"), and the superficial velocity of the fluidized incinerator is calculated based on the calculated or measured amount of exhaust gas.

(4) Compare the superficial velocity with the set minimum value, and if the superficial velocity is less than the minimum value, increase the opening of the control valve in the exhaust gas bypass path of the turbocharger, and The amount of exhaust gas to be sent is reduced to lower the rotational speed of the supercharger, and the opening degree of the surplus air control valve is reduced to maintain the pressure after the supply path, and the superficial velocity is set to a set maximum value. If the superficial velocity exceeds the maximum value, reduce the opening of the control valve in the exhaust gas bypass path of the turbocharger, increase the amount of exhaust gas sent to the turbocharger, and increase the rotation speed of the turbocharger. The present invention is characterized by increasing the opening degree of the surplus air control valve and maintaining the pressure after the supply path.

(5) If the amount of water injected into the furnace exceeds the upper limit of the target value, the compressed air sent from the supercharger through the supply path is branched, but by reducing the opening degree of the branch control valve, To reduce heat exchange in the air preheater, compressed air in the parallel flow line is increased to lower the furnace inlet air temperature, and if the amount of water injected into the furnace is below the lower limit of the target value, the supply path The compressed air sent through the line is branched, but by increasing the opening of the branch control valve, more compressed air is sent through the counterflow line to increase heat exchange in the air preheater. It is characterized by increasing the inlet air temperature.

Further, the apparatus for reducing the amount of N ₂ O emissions in exhaust gas is as described below.

(6) A device for reducing the amount of N ₂ O emissions in exhaust gas for controlling a fluidized fluidized incinerator that incinerates sludge as the main material to be incinerated, the feed being supplied to the fluidized fluidized incinerator. means for calculating the amount of exhaust gas discharged from the fluidized bed incinerator based on the supply amount of a plurality of types of supplies consisting of the object to be incinerated, water, fuel, and air; The superficial velocity of the fluidized incinerator is calculated based on the above, and if the superficial velocity is lower than the lower limit of the target value, the pressure of the compressed air supplied from the supercharger is reduced, and the superficial velocity is reduced to the target value. The present invention is characterized in that it includes means for increasing the pressure of compressed air supplied from the supercharger when the upper limit is exceeded.

(7) A device for reducing the amount of N ₂ O emissions in exhaust gas for controlling a fluidized fluidized incinerator that incinerates sludge as the main incineration target, and the amount of water injected into the furnace exceeds the upper limit of the target value. In this case, the furnace inlet air temperature is lowered, and when the amount of water injected into the furnace is lower than the lower limit of the target value, the furnace inlet air temperature is increased.

(8) A device for reducing the amount of N ₂ O emissions in exhaust gas for controlling a fluidized fluidized incinerator that incinerates materials to be incinerated, mainly sludge, the feed being supplied to the fluidized fluidized incinerator. Detecting the amount of exhaust gas discharged from the fluidized bed incinerator based on the supply amount of multiple types of supplies consisting of the incineration target, water, fuel, and air, and based on the detected amount of exhaust gas. The present invention is characterized by comprising means for calculating the superficial velocity of the fluidized incinerator.

(9) A device for reducing the amount of N ₂ O emissions in exhaust gas for controlling a fluidized fluidized incinerator that incinerates objects to be incinerated, mainly sludge, wherein the superficial velocity is set to a minimum value. If the superficial velocity is below the minimum value, increase the opening of the control valve in the exhaust gas bypass path of the turbocharger, reduce the amount of exhaust gas sent to the turbocharger, and reduce the rotation speed of the turbocharger. and reduce the opening degree of the surplus air control valve to maintain the pressure after the supply path, and compare the superficial velocity with the set maximum value, and if the superficial velocity exceeds the maximum value. If so, reduce the opening of the control valve in the middle of the exhaust gas bypass path of the turbocharger, increase the amount of exhaust gas sent to the turbocharger, increase the rotation speed of the turbocharger, and increase the opening of the excess air control valve. The apparatus is characterized by comprising means for maintaining the pressure after the supply path.

(10) A device for reducing the amount of N ₂ O emissions in exhaust gas for controlling a fluidized fluidized incinerator that incinerates materials to be incinerated, mainly sludge, wherein the amount of water injected into the furnace is below the upper limit of the target value. If it exceeds the limit, the compressed air sent from the turbocharger through the supply path is branched, but by reducing the opening degree of the branch control valve, it is possible to reduce the heat exchange in the air preheater so that the compressed air flows in parallel. The compressed air in the line is increased to lower the furnace inlet air temperature, and if the amount of water injected into the furnace is below the lower limit of the target value, the compressed air sent from the supercharger through the supply path is branched. However, by increasing the opening degree of the branch control valve, the amount of compressed air in the countercurrent line is increased to increase heat exchange in the air preheater, and the furnace inlet air temperature is increased. shall be.

It goes without saying that the present invention is not limited to the configurations described above and the configurations described in the embodiments described below, and that various changes can be made without departing from the technical idea of the present invention.

According to the present invention, in maintaining the incineration temperature necessary for N ₂ O decomposition, it is possible to ensure the amount of N ₂ O discharged without increasing costs by improving the heat resistance etc. of the fluidized incineration equipment. At the same time, the following effects can be obtained.

(1) When dehydrated sludge (cake) with low water content and a large amount of solid matter is incinerated, the amount of N ₂ O generated correlates with the amount of solid matter. Dehydrated sludge with low moisture content and high solid content has a high calorific value, so it tends to become self-combustible. During self-combustion, the temperature inside the furnace tends to rise, so the amount of water injected into the furnace increases. Although the temperature inside the furnace is suppressed by injecting water into the furnace, the amount of exhaust gas increases, so the space rate inside the furnace becomes faster and the gas residence time in the high temperature field inside the furnace becomes shorter. As will be described later, the decomposition of N ₂ O is reduced. Therefore, by increasing the operating pressure and slowing down the space rate to increase the residence time of the exhaust gas, the decomposition reaction of N ₂ O is maintained and the amount of N ₂ O emissions is not increased.

(2) However, as described in paragraph [0020], when the heat exchange efficiency of the air preheater increases and the furnace inlet air temperature rises to the point where the furnace temperature reaches the point where water is injected into the furnace again, As a result, the amount of gas generated in the furnace increases, so the gas residence time becomes shorter. In order to suppress the rise in the furnace inlet air temperature, it is conceivable to separately install an air cooler that can take in atmospheric air with a fan and exchange heat with the supply air, but this would increase the number of equipment. Therefore, without making major changes to the current equipment, as described in [0021], it is possible to change the heat exchange (parallel current/countercurrent) bias ratio of the air preheater using a damper, lowering the heat exchange efficiency, and reducing the combustion By lowering the air temperature, the temperature inside the furnace decreases, the amount of water injection decreases, the amount of gas generated decreases, and by maintaining the space rate and ensuring the gas residence time in the high temperature field inside the furnace, _N2 O decomposition is maintained.

A system configuration diagram illustrating an example of an N ₂ O emission reduction control device for adjusting combustion residence time in a fluidized incinerator according to the present invention. Diagram explaining an example of the correlation between the maximum temperature inside the furnace and the N ₂ O emission coefficient Diagram explaining the discrepancy between the in-furnace space rate and the correlation formula calculated N ₂ O and measured N ₂ O values Explanatory diagram of the relationship between exhaust gas heat amount and exchange heat amount of air preheater Flowchart explaining the N ₂ O emission reduction processing procedure executed by the control device

Hereinafter, one embodiment of an incinerator system to which the present invention is applied will be described in detail with reference to FIG. 1.

FIG. 1 is a system configuration diagram illustrating an example of an N ₂ O emission reduction control device for adjusting gas residence time in a fluidized incinerator according to the present invention. In FIG. 1, this system includes 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 supercharger 50, a starting blower 60, a white It consists of a smoke prevention fan 70 and a control device 90. Note that a white smoke preventer and a flue gas treatment tower are installed downstream of the supercharger 50, but their illustrations are omitted.

The incineration system 1 also includes a thermometer (T) 23, a thermometer (T) 24, a pressure gauge (P) 25, an air preheater cooling air amount meter (F) 26, an air preheater cooling air amount meter ( F) 27, and a supercharger rotation speed measuring device (R) 28. The incineration system 1 is also provided with a thermometer (T) 81, a supplied sludge amount meter (F) 82, a supplied water amount meter (F) 83, and a supplied fuel amount meter (F) 84.

The fluidized incinerator 2 described in one embodiment of the present invention is a supercharged fluidized incinerator. The fluidized fluid incinerator 2 can increase the combustion rate by supplying heated compressed air to the incinerator 2 and burning the objects to be incinerated in the incinerator 2 at high temperature and high pressure. ₂ It is possible to reduce the emission of harmful substances such as O. In addition, in the following description, the fluidized incinerator 2 is also simply called the incinerator 2.

In FIG. 1, a thick solid line with an arrow indicates a supply path (supply pipe) for sludge (cake), auxiliary fuel, air, water, or exhaust gas, and a broken line with an arrow indicates a bypass path.
A thin solid line with an arrow ((1) a line connected from the pressure gauge 25 to the control valve 48 (CV4), (2) a line from the control valve 48 (CV4) to the supercharger rotation speed measuring device 28, (3) A line connected from the supercharger rotational speed measurement device 28 to the air preheater cooling air amount measurement device 27, (4) a line connected from the air preheater cooling air amount measurement device 27 to the control valve 49 (CV5), and (5) temperature. A line connected from total 23 to control valve 17 (CV2) and control valve 22 (CV1), (6) a line connected from control valve 17 (CV2) to thermometer 24, (7) from thermometer 24 The line connected to the control valve 47 (CV3) and (8) the line connected from the air preheater cooling air amount measuring device 26 to the control valve 47 (CV3)) are, for example, This is a signal line that sends control signals, etc. to equipment.

Note that the measurement signal from each measuring meter and the control signal to each control valve are input to the control device and sent to the corresponding control valve 49 etc. after predetermined arithmetic processing. Therefore, most of the signal connection lines with the control device 90 are omitted.
Further, (1) a line connected from the pressure gauge 25 to the control valve 48 (CV4) indicates a control signal line that connects a pressure value signal to the control valve 48 (CV4) and adjusts its opening degree.

The fluidized incinerator 2 includes a fluidized bed 3, a preheated air intake 4, and a starting burner 5 inside the furnace. Additionally, a sludge inlet (not shown) that takes in sludge supplied via a valve 19 from a supply path (sludge supply pipe) 11 connected to the sludge (cake) supply device 10 , and a supply connected to the water supply device 15 . A water (water injection) inlet (not shown) that takes in water (water injection) supplied from a channel (water supply pipe) 16, and auxiliary fuel supplied from a supply channel (fuel supply pipe) 21 connected to a fuel supply device 20. A fuel intake port (not shown) is provided to take in the fuel.

The sludge (cake) supply device 10 sequentially supplies cakes of sewage sludge sent from a sewage treatment facility (not shown) and stored in a hopper (not shown) to the incinerator 2 through a supply pipe 11.

The water supply device 15 adjusts the combustion temperature in the incinerator 2 by feeding water (water injection) into the incinerator 2 from the connected supply pipe 16 . The fuel supply device 20 adjusts the combustion temperature in the incinerator 2 by feeding auxiliary fuel into the incinerator 2 from a 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 degrees are adjusted according to a control signal output from the control device 90.

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.

The thermometer (T) 24 measures the temperature of residual heated air supplied into the fluidized incinerator 2 from the air preheater 30. The thermometer 24 is connected to the control device 90 and outputs the measured temperature value to the control device 90.

The pressure gauge (P) 25 measures the pressure inside the fluidized 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 cooling air amount measuring device (F) 26 measures the amount of compressed air supplied from the supercharger 50 to the air preheater 30. The air preheater cooling air amount measuring device 26 is connected to the control device 90 and outputs the measured compressed air amount value to the control device 90.

The air preheater air amount measuring device (F) 27 measures the amount of compressed air supplied from the supercharger 50. The air preheater air amount measuring device 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 (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 value to the control device 90.

The air preheater 30 receives exhaust gas sent from the fluidized fluidized incinerator 2 through the supply path 58, and compressed air sent from the supercharger 50 through the supply path 56, the branch supply path 56a, and the branch supply path 56b. is heat exchanged. The heat-exchanged air is then supplied into the incinerator 2 from the preheated air intake 4 via the supply path 29.

The dust collector 40 separates and collects solid components such as ash contained in the exhaust gas from the exhaust gas discharged from the air preheater 30 sent from the supply path 31, and collects the exhaust gas from which the solid components such as ash have been removed. , to the supercharger 50 via the supply path 41, and the sent exhaust gas is sent from the supercharger 50 to the white smoke prevention preheater via the supply path 42.

The supercharger 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 to the supercharger 50 via the supply path 41 and rotates at a high speed, thereby causing the compressor 53 to rotate at a high speed. The compressor 53 compresses the air taken into the supercharger 50, and sends the compressed air to the air preheater 30 via a supply path 56, a branch supply path 56a, and a branch supply path 56b. In the air preheater 30 , exhaust gas and compressed air exchange heat, and the heated compressed air is sent to the preheated air intake 4 of the incinerator 2 via the supply path 29 .

The supply path 56 is provided with a control valve 47 (CV3) between the branch supply path 56a and the branch supply path 56b. The control valve 47 (CV3) is connected to a control device 90, and its opening degree is adjusted in accordance with a control signal output from the control device 90.
By adjusting the opening degree, the amount of compressed air supplied to the branch supply passage 56a supplied to the upper side of the air preheater 30 and the branch supply passage 56b supplied to the lower side of the air preheater 30 is adjusted.

The starting blower 60 supplies the air taken in from the supply path 61 to the air supply path 56 and from the supply path 62 to the supercharger 50 when the incineration system 1 is started. Reference numeral 63 is a check valve provided in the supply path 62.

After startup, when fluidized air from the compressor 53 of the supercharger 50 can be secured using exhaust gas from the fluidized incinerator 2, the supply of atmosphere (air) from the startup blower 60 is stopped and the atmosphere is transferred to the supply path 65. The fuel is then switched to be supplied to the supercharger 50 from there. Reference numeral 66 denotes a control valve provided in the supply path 65, which is connected to a control device 90 and whose opening degree is adjusted in accordance with a control signal output from the control device 90.

The white smoke prevention fan 70 sends the air taken in to a white smoke prevention device (not shown).
The white smoke preventer exchanges heat with the exhaust gas discharged from the supercharger 50 supplied via the supply path 42 to raise the temperature of the air sent from the white smoke preventive fan 70 that takes in the atmosphere. 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 flue gas from the flue gas.

A bypass passage 43 provided between the supply passage 41 and the supply passage 42 is provided with a supercharger exhaust gas bypass control valve 48 (CV4). This supercharged exhaust gas bypass control valve 48 (CV4) is connected to a control device 90, and its opening degree is adjusted in accordance with a control signal output from the control device 90.
By adjusting the opening degree, the amount of exhaust gas sent from the supply path 41 to the supercharger 50 is adjusted. When the opening degree of the supercharged exhaust gas bypass control valve 48 (CV4) is increased, the amount of exhaust gas sent to the supercharger 50 is reduced.

Then, 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 supercharger 50. Further, a bypass passage 57 provided between the air supply passage 56 and the supply passage 71 is provided with an excess air control valve 49 (CV5).

The surplus air control valve 49 (CV5) is connected to a control device 90, and its opening degree is adjusted in accordance with a control signal output from the control device 90. By adjusting this opening degree, the amount of compressed air sent from the supercharger 50 to the supply path 56 is adjusted.
For example, if the opening degree 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 will increase, so the amount of compressed air sent from the supply path 56 to the air preheater 30 will be reduced. Ru.
Then, the amount of compressed air sent from the supply path 56 to the air preheater 30 is adjusted.

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 functions for data processing such as ROM, RAM memory, data storage section, input/output section, etc., as well as a first calculation section (gas amount calculation section) 91 and a second calculation section that characterize the present invention. section (space rate calculation section) 92.

The first calculation unit 91 operates on a plurality of air supply sources such as the supply device 10 for the incineration object, the water supply device 15, the fuel supply device 20, and the supercharger 50, which are the supplies to be supplied to the fluidized incinerator 2. The amount of exhaust gas discharged from the fluidized bed incinerator is calculated based on the amount of seed feed. The second calculation unit 92 calculates the space rate of the fluidized incinerator based on the calculated amount of exhaust gas.

FIG. 3 is a diagram illustrating the deviation [%] between the calculated N ₂ O obtained from the correlation equation in FIG. 2 and the N ₂ O measurement value of the exhaust gas measured by the analyzer with respect to the space rate in the furnace [m/sec]. . As shown in FIG. 3, the deviation [%] between the correlation formula calculated N ₂ O and the measured N ₂ O value with respect to an increase or decrease in the in-furnace space rate [m/sec] can be approximated by a substantially linear straight line.
There is no deviation near the in-furnace space rate of 0.73 m/sec, and the calculated N ₂ 0 from the correlation formula and the measured N ₂ O value match. In a range larger than this, the deviation increases in the positive direction, and the measured N ₂ O value becomes larger than the calculated N ₂ O. In a range where the space rate is large, the residence time of gas in the furnace decreases, resulting in a decrease in the actual discharged N _{2 O.} This means that the amount of O will increase. On the other hand, in a range where the space rate in the furnace is smaller than around 0.73 m/sec, the deviation increases in the negative direction, and the measured N ₂ O value becomes smaller than the calculated N ₂ O. As the time increases, it means that the actual amount of discharged N ₂ O decreases. From this, by reducing the in-furnace space rate [m/sec] as much as possible, the amount of N ₂ O emissions can be suppressed.

Figure 4 is an explanatory diagram of the relationship between the amount of heat exchanged by the air preheater and the amount of heat exchanged between the exhaust gas and the air preheater, which was explained in section (2) of the effects of the invention. The lower curve shows the amount of heat exchanged by the air preheater when the proportion of cooling air in the parallel flow line is 40%. The exhaust gas calorific value on the horizontal axis is shown in terms of the amount of air supplied to the fluidized bed incinerator. Bias ratio adjustment is performed to change the ratio of the amount of air supplied to the furnace between the parallel flow line and the countercurrent line.For example, when the temperature inside the furnace has risen and it is difficult to lower the temperature inside the furnace even if water is being injected into the furnace. In addition, increasing the proportion of air in the cocurrent line reduces the amount of heat exchanged in the air preheater, lowering the temperature of the supply air, and lowering the furnace temperature to maintain the appropriate combustion temperature. In addition to the water injection means, by providing a means for lowering the temperature of the air supplied to the furnace, it is possible to maintain the furnace temperature at an appropriate combustion temperature and prevent an increase in exhaust gas due to water injection into the furnace. N ₂ O decomposition can be maintained appropriately by controlling the space rate in the furnace and ensuring the residence time of the gas generated in the furnace.

FIG. 5 is a flowchart illustrating an example of suppressing exhaust N ₂ O by the control device 90 shown in FIG. The control device 90 repeatedly executes this process at a predetermined period, typically every few seconds.

When the incinerator starts operating and the start time of the predetermined cycle has arrived, this control starts (START). When starting, first, the exhaust gas mass flow rate is measured or calculated (step 1, hereinafter referred to as S-1).

Next, the exhaust gas volumetric 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).

The in-furnace space rate S1 is compared with the set minimum value S1min (S-4), and 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 middle of the bypass passage 43, reduce the amount of exhaust gas sent to the supercharger 50, and lower the rotation speed of the supercharger 50. Since there is a risk that the rate may become too large than the appropriate range for decomposing N ₂ O, the compressed air sent to the air preheater 30 via the supply path 56 is further reduced by reducing the opening degree of the surplus air control valve 49. There is an example in which the pressure after the supply path 56 is maintained.

If S1<S1min is not satisfied (S1≧S1min) in (S-4), it is determined whether S1max<S1 (S-6). If S1max<S1, an operation is performed to increase P1 (S-7). The operation of increasing P1 is to reduce the opening degree of the control valve 48 in the middle of the bypass passage 43, increase the amount of exhaust gas sent to the supercharger 50, and increase the rotation speed of the supercharger 50, but this reduces the space inside the furnace. While the rate is low enough to decompose N ₂ O, the fluidized bed 3 in the fluidized incinerator may not be able to flow sufficiently, leading to incomplete combustion of the material to be incinerated. There is an example in which the pressure of the compressed air sent to the air preheater 30 is maintained at the pressure after the supply path 56 by increasing the opening degree of the surplus air control valve 49. When S1max<S1 is not satisfied (when S1min≦S1≦S1max), the process ends (END).

On the other hand, in response to the start of the process (START), it is determined whether F4max<F4 or not (S-8), and if F4max<F4, an operation to lower T2 is executed (S-9). The operation of reducing T2 means that the compressed air sent from the supercharger 50 through the supply path 56 is branched into the supply path 56a and the supply path 56b, but by reducing the opening degree of the control valve 47. , the amount of compressed air passed to the supply path 56a is increased, that is, the amount of compressed air in the parallel flow line is increased so that heat exchange within the air preheater 30 can be reduced, and the supply air to the fluidized fluid incinerator 2 is supplied to the furnace inlet. There is an example of lowering the air temperature T2. If it is determined in (S-8) that F4max<F4 is not true, it is determined whether F4min<F4 (S-10), and if F4min<F4, an operation to increase T2 is executed (S-11). The operation of increasing T2 means that the compressed air sent from the supercharger 50 through the supply path 56 is branched into the supply path 56a and the supply path 56b, but by increasing the opening degree of the control valve 47. , the amount of compressed air passed to the supply path 56b is increased, that is, the amount of compressed air in the countercurrent line is increased so that heat exchange within the air preheater 30 can be increased, and the supply air to the fluidized fluid incinerator 2 is supplied to the furnace inlet. There is an example of increasing the air temperature T2. If F4min<F4, the operation ends (END).

By repeatedly performing the above operation at a predetermined period, the amount of N ₂ O in the exhaust gas can be reduced.

1: Incineration system 2: Fluidized incinerator 3: Fluidized bed 4: Preheating air intake 5: Starting burner 10: Sludge supply device 11: Sludge supply path 15: Water supply device 16: Water supply path 17: Control valve (CV2 : Supply water 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 amount measuring device (F: F1 measurement)
27: Air preheater cooling air amount measuring device (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: Supercharger 60: Start-up blower 70: White smoke prevention fan 81: Thermometer (T: T3 measurement)
82: Supply sludge amount measuring device (F: F3 measurement)
83: Supply water amount measuring device (F: F4 measurement)
84: Supply fuel amount measuring device (F: F5 measurement)
90: Control device (compares each measured value with set value/threshold value and calculates appropriate control value)
91: Gas amount calculation unit 92: Superficial velocity calculation unit

Claims (10)

A method for reducing N ₂ O emissions in exhaust gas for controlling a fluidized fluidized incinerator that incinerates sludge as the main incineration target, the method comprising:
Measuring the supply amount of a plurality of types of supplies, which are the supplies to be supplied to the fluidized incinerator, consisting of the material to be incinerated, water, fuel, and air,
Based on the measurement results, calculate the amount of exhaust gas discharged from the fluidized incinerator,
Calculating the superficial velocity of the fluidized incinerator based on the calculated exhaust gas amount,
If the superficial velocity is below the lower limit of the target value, the pressure of the compressed air supplied from the supercharger is reduced, and if the superficial velocity exceeds the upper limit of the target value, the compressed air supplied from the supercharger is reduced. A method for reducing N 2 O emissions in exhaust gas, the method comprising increasing the pressure of N ₂ O in exhaust gas. If the amount of water injected into the furnace exceeds the upper limit of the target value, the furnace inlet air temperature will be lowered,
2. The method for reducing N ₂ O emissions in exhaust gas according to claim 1, further comprising increasing the furnace inlet air temperature when the amount of water injected into the furnace is less than the lower limit of the target value. Detecting the amount of exhaust gas discharged from the fluidized fluidized incinerator based on the supply amount of multiple types of supplies, which are the materials to be incinerated, water, fuel, and air, which are supplied to the fluidized fluidized incinerator. ,
The method for reducing N ₂ O emissions in exhaust gas according to claim 1 or 2, further comprising calculating the superficial velocity of the fluidized incinerator based on the detected amount of exhaust gas. The superficial velocity is compared with the set minimum value, and if the superficial velocity is lower than the minimum value, the opening degree of the control valve in the exhaust gas bypass path of the turbocharger is increased to reduce the exhaust gas sent to the turbocharger. reducing the amount of excess air to lower the rotational speed of the supercharger and reducing the opening degree of the surplus air control valve to maintain the pressure after the supply path;
The superficial velocity is compared with the set maximum value, and if the superficial velocity exceeds the maximum value, the opening degree of the control valve in the exhaust gas bypass path of the turbocharger is reduced to reduce the exhaust gas sent to the turbocharger. Any one of claims 1 to 3, characterized in that the amount is increased to increase the rotational speed of the supercharger and the opening degree of the surplus air control valve is increased to maintain the pressure after the supply path. The method for reducing N ₂ O emissions in exhaust gas according to claim 1. When the amount of water injected into the furnace exceeds the upper limit of the target value, the amount of water in the air preheater is reduced by reducing the opening degree of the branch control valve that branches the compressed air sent from the supercharger through the supply path. To reduce heat exchange, increase the compressed air in the parallel flow line and lower the furnace inlet air temperature.
When the amount of water injected into the furnace is less than the lower limit of the target value, by increasing the opening degree of the branching control valve that branches the compressed air sent from the supercharger through the supply path, the air preheater N ₂ O emissions in exhaust gas according to any one of claims 1 to 4, characterized in that the compressed air in the countercurrent line is increased to increase the furnace inlet air temperature so as to increase heat exchange within the furnace. Reduction method. A device for reducing N ₂ O emissions in exhaust gas for controlling a fluidized fluidized incinerator that incinerates sludge as the main incineration target, comprising:
a feed measuring means for measuring the amount of a plurality of feeds to be supplied to the fluidized incinerator, which are the objects to be incinerated, water, fuel, and air;
Exhaust gas amount calculation means for calculating the amount of exhaust gas discharged from the fluidized incinerator based on the measurement result with the feed measurement means;
superficial velocity calculation means for calculating the superficial velocity of the fluidized bed incinerator based on the exhaust gas amount calculated by the exhaust gas amount calculation means;
If the superficial velocity is below the lower limit of the target value, the pressure of the compressed air supplied from the supercharger is reduced, and if the superficial velocity is above the upper limit of the target value, the pressure of the compressed air is supplied from the supercharger. A device for reducing the amount of N ₂ O emissions in exhaust gas, comprising a compressed air pressure adjusting means for increasing the pressure of compressed air. If the amount of water injected into the furnace exceeds the upper limit of the target value, reduce the furnace inlet air temperature,
7. The method according to claim ₆ , further comprising a furnace inlet air temperature adjusting means for increasing the furnace inlet air temperature when the amount of water injected into the furnace is less than the lower limit of the target value. Equipment to reduce. Detecting the amount of exhaust gas discharged from the fluidized fluidized incinerator based on the supply amount of a plurality of types of supplies, which are the materials to be incinerated, water, fuel, and air, which are supplied to the fluidized fluidized incinerator. Exhaust gas amount detection means;
and a superficial velocity calculation means for calculating the superficial velocity of the fluidized incinerator based on the amount of exhaust gas detected by the exhaust gas amount detection means. A device that reduces N ₂ O emissions. The superficial velocity is compared with a set minimum value, and if the superficial velocity is less than the minimum value, the opening degree of a valve in the middle of the exhaust gas bypass path of the turbocharger is increased and the exhaust gas is sent to the turbocharger. Compare the superficial velocity and the set maximum value with an excess air control valve that reduces the amount of exhaust gas, lowers the rotation speed of the supercharger, and reduces the opening of the valve to maintain the pressure after the supply path. and an opening adjustment valve provided in the middle of the exhaust gas bypass passage that operates to reduce the opening degree of the valve in the exhaust gas bypass passage of the supercharger when the superficial velocity exceeds the maximum value,
The amount of exhaust gas sent to the supercharger is increased to increase the number of rotations of the supercharger, and the opening degree of the surplus air control valve is increased to maintain the pressure after the supply path. An apparatus for reducing the amount of N ₂ O emissions in exhaust gas according to any one of claims 6 to 8. comprising a branch adjustment valve that branches compressed air passing through the supply path from the supercharger,
If the amount of water injected into the furnace exceeds the upper limit of the target value, reduce the opening degree of the branch control valve to reduce the opening degree of the branch control valve to send compressed air from the supercharger through the supply path and branched by the branch control valve. In order to reduce heat exchange in the air preheater, compressed air in the parallel flow line is increased to lower the furnace inlet air temperature.
When the amount of water injected into the furnace is less than the lower limit of the target value, the branched compressed air sent from the supercharger through the supply path is increased to an air preheater by increasing the opening degree of the branch control valve. The amount of N ₂ O emissions in the exhaust gas according to any one of claims 6 to 9 is increased by increasing the amount of compressed air in the countercurrent line to increase the heat exchange within the furnace to increase the temperature of the furnace inlet air. Equipment to reduce.

Images