JP2023151255A - Method of reducing emission of n2o in exhaust gas, and control device - Google Patents

Abstract

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

Description

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 flow state of a fluidized medium such as sludge, and in particular, N ₂ O, which is a greenhouse gas, 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 stirs and incinerates materials to be incinerated, such as garbage, together with a fluid medium. The fluidization state in a fluidized bed incinerator depends on the air supplied to the furnace (also simply referred to as supply air, combustion air, fluidized air, or preheated air), the amount of materials to be incinerated, auxiliary fuel, etc., and the temperature and pressure inside the furnace. It is important to stabilize the flow state and optimize the combustion state in order to increase 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 one of the greenhouse gases generated from the exhaust gas when incinerating organic components contained in materials to be incinerated. There is.

For example, in a fluidized fluidized incinerator, a method of adjusting the amount of air supplied into the furnace to make the fluidized medium flow according to the brightness inside the furnace, the amount of supplied material to be incinerated, the temperature, the oxygen concentration, or the pressure inside the furnace. 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, particularly N ₂ O (hereinafter referred to as N ₂ O) and NOx emissions, a method is known in which a slurry mixture of an ammonia-based reducing agent and a porous fluid medium is injected into the furnace. (See Patent Document 3).

Patent No. 3108742 Japanese Patent Application Publication No. 2004-125332 Patent No. 5640120 JP2020-159655A

The amount of sewage sludge discharged is increasing year by year, and about 70% of it is incinerated. When sludge is combusted, it has a very high nitrogen content compared to other fuels, and there are concerns that N ₂ O will be emitted during the incineration process.
A supercharged fluidized fluid incinerator system can reduce N ₂ O contained in combustion exhaust gas by creating a high-temperature region through combustion under pressure.
In a supercharged fluidized incinerator, combustion (sludge, etc.) is combusted in a fluidized bed at a temperature of 870 to 880°C, for example, at _a temperature of 870 to 880°C. ) is decomposed. Note that the greenhouse effect of N ₂ O is 298 times the amount of CO ₂ equivalent).
The temperature of the incinerator is adjusted depending on the properties of the dehydrated sludge to maintain the temperature inside the furnace, either by supplying auxiliary fuel for combustion (assisted combustion state), or by not supplying auxiliary fuel if the dehydrated sludge has low water content and is easily combustible. The temperature is controlled by combustion (self-combustion state), which cools down the furnace by injecting water when the temperature inside the furnace rises.

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 fluidized incinerator, a superficial velocity suitable for operation at a predetermined incineration load is set, and the size of the incinerator is adjusted so that the material to be incinerated is incinerated at the set superficial velocity. The particle size etc. of the fluidizing 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 3 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. 3, 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. 3 . 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 there will be problems caused by the increase in the temperature of the exhaust gas flowing into the air preheater and 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.Operating management measures must also be taken separately for _N2O decomposition. There is a need.

The purpose of the present invention is to maintain the incineration temperature necessary for N ₂ O decomposition by improving the heat resistance of incineration equipment, thereby achieving fluidized incineration that ensures the amount of N ₂ O discharged without increasing costs. The object of the present invention is to provide an operating method and apparatus for a furnace, and more specifically, a method and apparatus for reducing _N2O emissions that realize operating indicators for adjusting gas residence time in a fluidized fluidized incinerator.

Furthermore, in supercharged fluidized incineration that incinerates sludge with low moisture content, under natural conditions, the temperature inside the furnace increases and the amount of water injected increases, which shortens the residence time of exhaust gas inside the furnace and increases N ₂ O. Therefore, by increasing the pressure with a supercharger to suppress the superficial velocity in the furnace (hereinafter referred to as space rate), and increasing the residence time of the exhaust gas generated in the furnace, the amount of N ₂ O emissions can be suppressed. With the goal.

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 emissions 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 residence time of the gas in the furnace: (1) increasing the size of the furnace; and (2) decreasing the exhaust gas space rate 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 determining the space rate from each supply amount indicated by each measuring device, first calculate the mass flow rate from each supply amount, convert it to a volumetric flow rate, obtain the gas generation amount, and 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.

Since (1) above leads to an increase in equipment costs, (2) above 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. That is, by increasing the residence time of the exhaust gas generated in the furnace, the space rate for suppressing the decomposition of N ₂ O is maintained.

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. 3 described above. In the present invention, N ₂ O is reduced by employing 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 uses the above-mentioned "adjustment using operating pressure" technology 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. The present invention is characterized by a structure and method for reducing N ₂ O by applying the above.

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 emissions.

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.

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.

Methods for reducing N ₂ O emissions in exhaust gas in a fluidized fluidized incinerator that incinerates sludge as the main incineration target are as follows [1] to [3].
[1] A method for reducing 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: Based on the above, calculate the amount of exhaust gas discharged from the fluidized incinerator, or directly measure the amount of exhaust gas, calculate the superficial velocity of the fluidized incinerator based on the calculated or measured amount of exhaust gas, and perform supercharging. A method for reducing N ₂ O emissions in exhaust gas, the method comprising controlling the superficial velocity by adjusting the pressure of compressed air supplied from a machine.
[2] Compare the superficial velocity with the set minimum value, and 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, 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 method for reducing the amount of N ₂ O emissions in exhaust gas according to [1], characterized in that the pressure after the supply path is maintained by increasing the amount of air and increasing the opening degree of the surplus air control valve.
[3] In the relationship between the superficial velocity and the discrepancy between the correlation formula calculated N ₂ O and the measured N ₂ O value, the superficial velocity is controlled to such a value that the discrepancy is 0 or less [1] or [ 2], the method for reducing the amount of N ₂ O emissions in exhaust gas.

The following [4] to [6] describe devices for reducing N ₂ O emissions in exhaust gas in a fluidized fluidized incinerator that incinerates sludge as the main incineration target.
[4] A method for reducing 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: Based on the above, calculate the amount of exhaust gas discharged from the fluidized incinerator, or directly measure the amount of exhaust gas, calculate the superficial velocity of the fluidized incinerator based on the calculated or measured amount of exhaust gas, and perform supercharging. A control device that operates based on a control program for reducing the amount of N ₂ O emissions in exhaust gas, characterized in that the pressure of compressed air supplied from the machine is adjusted to control the superficial velocity.
[5] Compare the superficial velocity with the set minimum value, and 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, 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 control device according to [4], characterized in that the pressure after the supply path is maintained by increasing the amount of air and increasing the opening degree of the surplus air control valve.
[6] In the relationship between the superficial velocity and the discrepancy between the correlation formula calculated N ₂ O and the measured N ₂ O value, the superficial velocity is controlled to be such that the discrepancy is 0 or less [4] or [4] 5]. The control device according to item 5.

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.

When dehydrated sludge (cake) with a low water content and a large amount of solids is incinerated, the amount of N ₂ O generated correlates with the amount of solids. 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 does not increase.

It is a schematic diagram showing an example of the incineration system including the control device of the fluidized incinerator in a 1st embodiment. It is a sectional view showing an example of the structure of an air preheater. It is a figure explaining the correlation example of the maximum temperature in a furnace, and a _N2O emission coefficient. FIG. 4 is a diagram illustrating the deviation [%] between the calculated N ₂ O obtained from the correlation equation in FIG. 3 and the N ₂ O measurement value of the exhaust gas measured by the analyzer with respect to the in-furnace space rate [m/sec]. FIG. 3 is an explanatory diagram showing the flow of calculations executed by the control device.

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

The incineration system 1 shown in FIG. 1 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 startup blower 60, It consists of a white smoke prevention fan 70 and a control device 90.
Note that the white smoke prevention fan 70 sends the air taken in to the white smoke preventer 75 located downstream, and the white smoke preventer 75 combines the air sent from the white smoke prevention fan 70 with the excess air supplied via the supply path 42. The temperature is increased by exchanging heat with the exhaust gas discharged from the feeder 50. The heated air is sent toward the flue gas treatment tower 80 located downstream.
The incineration system 1 also includes thermometers 23 and 24, a pressure gauge 25, air preheater air amount measuring devices 26 and 27, and a supercharger rotation speed measuring device 28.
F2 written on the air preheater air amount measuring device 27 in FIG. 1 represents the amount of compressed air supplied from the supercharger 50 to the air preheater 30.

For example, in the embodiment of the present invention, the fluidized incinerator 2 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 O emissions of harmful substances can be reduced.
In addition, in the following description, the fluidized incinerator 2 is also simply called the incinerator 2.

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 (for example, <1> a line connected from the pressure gauge 25 to the control valve 48 (CV4), <2> a line connected from the control valve 48 (CV4) to the supercharger rotation speed measuring device 28, 3> Wires connected from the supercharger rotation speed measuring device 28 to the air preheater air amount measuring device 27, <4> Wires connected from the air preheating air amount measuring device 27 to the control valve 49 (CV5), <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 lines connected to the control valve 47 (CV3), the lines connected from the air preheater air amount measuring device 26 to the control valve 47 (CV3), etc.) are connected to these control valves from the control device. Shows the signal line that sends the signal.
For example, the control device 90 receives a pressure value from the pressure gauge 25, sends an opening command signal to the control valve 48 (CV4) based on the pressure value, and adjusts the opening of the control valve 48.

The fluidized incinerator 2 includes a fluidized bed 3, a preheating air intake 4, and a starting burner 5 inside the furnace. Additionally, a sludge inlet (not shown) that takes in sludge supplied from a supply path (sludge supply pipe) 11 connected to the sludge (cake) supply device 10, and a supply path (water supply pipe) connected to the water supply device 15 are also provided. ) 16, a water (water injection) inlet (not shown) that takes in water (water injection) supplied from An entrance (not shown) is provided.
A sludge (cake) supply device 10 sequentially supplies cakes of sewage sludge sent from sewage treatment equipment 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, and the fuel supply device 20 feeds water (water injection) into the incinerator 2 from the connected supply pipe 21. The combustion temperature in the incinerator 2 is adjusted by sending the auxiliary fuel into the incinerator 2.
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 23 measures the temperature of the fluidized bed 3 provided in the fluidized incinerator 2 . The thermometer 23 is connected to the control device 90 and outputs the measured temperature value to the control device 90.
The thermometer 24 measures the temperature of 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 25 measures the pressure of the exhaust gas 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 air amount measuring device 26 measures the amount of compressed air supplied from the supercharger 50 to the air preheater 30. The air preheater 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 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 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.

FIG. 2 is a sectional view showing an example of the structure of the air preheater.
The air preheater 30 consists of a cylindrical housing 30a, and the interior of the housing 30a is partitioned by a partition plate 30c, and an upper parallel flow type heat exchange chamber 30d and a lower countercurrent type heat exchange chamber 30e are provided. It consists of
30f is a high temperature side tube plate, 30g is a low temperature side tube plate, 30h is a heat exchanger tube, 30i is a baffle plate, 30j is an exhaust gas discharge chamber, 30k is a compressed air introduction that sends compressed air to the upper parallel flow type heat exchange chamber 30d. The header 30m is a compressed air introduction header that sends compressed air to the lower countercurrent heat exchange chamber 30e, 30n is a hot fluid discharge header, F1 is a high temperature exhaust gas, and F2 is a low temperature exhaust gas.
The high temperature exhaust gas F1 supplied from the fluidized incinerator 2 to the air preheater 30 via the supply path 58 and the upper heat exchange chamber 30d are separated by a high temperature side tube plate 30f, and the upper heat exchanger is separated from the exhaust gas discharge chamber 30j. The chamber 30d and the lower countercurrent heat exchange chamber 30e are separated by the low temperature side tube plate 30g.
A large number of heat transfer tubes 30h are installed in the heat exchange chambers (heat exchange chamber 30d and heat exchange chamber 30e), and the upper and lower ends thereof are connected to the high temperature side tube plate 30f and the low temperature side tube plate 30g, respectively. There is. The high-temperature exhaust gas F1 flowing into the heat exchange chambers (heat exchange chambers 30d and 30e) through the heat exchanger tubes 30h is sent from the fluidized bed incinerator 2 via the supply path 58.
Furthermore, a partition plate 30c is attached to the middle part of the heat exchange chamber, dividing the heat exchange chamber into two parts: an upper heat exchange chamber 30d and a lower heat exchange chamber 30e. Several baffle plates (baffle plates) 30i are arranged in the upper heat exchange chamber 30d and the lower heat exchange chamber 30e.

In the upper parallel flow type heat exchange chamber 30d, air and exhaust gas flow in the same direction, and the amount of heat exchange is small, so the air discharged from the air preheater is difficult to warm. In 30e, the flow of air and exhaust gas are reversed, and the amount of heat exchanged is large, so the air coming out is easily warmed.
In the thermal fluid discharge header 30n at the position where the supply path 29 is connected, the preheated air flowing from the upper parallel flow type heat exchange chamber and the preheated air flowing from the lower counter flow type heat exchange chamber are connected. The mixed preheated air is supplied to the incinerator.

The air preheater 30, which is an embodiment of the present invention, collects exhaust gas sent from the fluidized incinerator 2 through the supply path 58, and from the supercharger 50 through the supply path 56, branch supply path 56a, and branch supply path 56b. Heat is exchanged with the compressed air sent in.
The heat-exchanged air is then supplied into the incinerator 2 from the preheated air intake port 4 from the preheated fluid discharge header 30n 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. , the exhaust gas is sent to the supercharger 50 via the supply path 41, and the sent exhaust gas is sent from the supercharger 50 to the white smoke preventer 75 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 the supply path 56, branch supply path 56a, and 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 port 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 for adjusting the amount of compressed air supplied to the upper heating chamber 30d and the lower heating chamber 30e of the air preheater 30. It is being 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 startup blower 60 supplies air taken in when the incineration system 1 is started from a supply path 61 to the air supply path 56 and from a supply path 62 to the supercharger 50. 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 the white smoke prevention device 75 via the supply path 71.
The white smoke preventer 75 exchanges heat with the air sent from the white smoke preventive fan 70 that takes in atmospheric air and the exhaust gas discharged from the supercharger 50 that is supplied via the supply path 42 to raise the temperature. The heated air is sent toward the flue gas treatment tower 80.
The flue gas treatment tower 80 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 control valve 48 (CV4) that regulates the amount of exhaust gas supplied from the supercharger.
The control valve 48 (CV4) is connected to a control device 90, and its opening degree is adjusted according to 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. For example, when the opening degree of the control valve 48 (CV4) is increased, part of the exhaust gas sent to the turbocharger 50 from the supply path 41 that supplies exhaust gas from the dust collector 40 to the turbocharger is transferred from the turbocharger 50 to the white smoke preventer. 75, the amount of exhaust gas sent from the supply path 41 to the supercharger 50 is reduced. Then, the pressure in the compressed air supply path downstream of 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.
For example, when it is desired to increase the pressure of the supply air in the air preheater 30, the control valve 48 (CV4) is closed and the rotation speed of the supercharger 50 is increased. Conversely, when it is desired to reduce the pressure of the supplied air, the opening degree of the control valve 48 (CV4) is increased to reduce the rotation speed of the supercharger.

Further, the bypass passage 53 provided between the air supply passage 56 and the supply passage 71 is provided with a control valve 49 (CV5) that adjusts the amount of surplus air.
The surplus air control valve 49 (CV5) is connected to a control device 90, and its opening degree is adjusted according to a control signal of an opening degree command output from the control device 90.
When adjusting the pressure of the supply air, the pressure of the compressed air sent from the supercharger 50 to the supply path 56 is adjusted by adjusting the opening degree, and the amount of compressed air is adjusted.

For example, when the mass flow rate of compressed air is constant, the volumetric flow rate decreases when the pressure is high, so the opening degree of the surplus air control valve 49 (CV5) is increased and the surplus air is transferred from the bypass path 53 to the supply path 71. By releasing the air and releasing the pressure, the volumetric flow rate of the compressed air sent from the supply path 56 to the air preheater 30 is increased, whereas when the pressure is low, the volumetric flow rate increases, so surplus air adjustment is performed. By reducing the opening degree of the valve 49 (CV5) and maintaining the pressure without letting excess air escape from the bypass path 53 to the supply path 71, the volumetric flow rate of compressed air sent from the supply path 56 to the air preheater 30 is reduced. let
In other words, since the amount of flowing air is affected by changes in the volumetric flow rate due to changes in the pressure of the flowing air, by adjusting the opening degree of the surplus air control valve 49 (CV5), the amount of flowing air can be kept within a certain range and the fluidized air incineration can be carried out. It is possible to stabilize the fluidized state of the fluidized bed in the furnace and to optimize the combustion state.

The control device 90 includes, for example, a PLC (Programmable Logic Controller), and operates based on a control program executed by the PLC.
The control device 90 receives signals from various sensors (thermometer, pressure gauge, air preheater air amount measuring device, supercharger rotation speed measuring device, etc.), and uses the built-in control program to adjust the received signals to Sends corresponding control signals to various devices (control valves) to control various devices.

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. 4 is a diagram illustrating the deviation [%] between the calculated N ₂ O obtained from the correlation equation in FIG. 3 and the N ₂ O measurement value of the exhaust gas measured by the analyzer with respect to the in-furnace space rate [m/sec]. . As shown in FIG. 4, the deviation [%] between the correlation formula calculated N ₂ O and the measured N ₂ O value with respect to the 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 N ₂ O calculated from the correlation equation 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 the gas in the furnace decreases, so the actual discharged N ₂ 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.

FIG. 5 is a flowchart illustrating an example of suppressing exhaust N ₂ O by the control device 90 shown in FIG. 1. 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 S1).

Next, the exhaust gas volumetric flow rate is calculated from the furnace temperature T3 and the furnace pressure P1 (S2), and then the furnace space rate S1 is calculated (S3).

The in-furnace space rate S1 is compared with the set minimum value S1min (S4), and if S1<S1min, an operation to lower P1 is executed (S5). 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 does not hold in (S4) (S1≧S1min), it is determined whether S1max<S1 (S6). If S1max<S1, an operation is performed to increase P1 (S7). 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. If S1max<S1, the process ends (END).
By periodically performing the above steps, the system pressure in the incineration system 1 using a supercharged fluidized fluid incinerator is adjusted, the space rate in the furnace is controlled, and the generation of N ₂ O is suppressed. It can be maintained during the residence time of the gas accompanying gas generation in the furnace.

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

Claims (6)

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:
Calculating the amount of exhaust gas discharged from the fluidized incinerator based on the gas generated in the fluidized incinerator, or directly measuring the amount of exhaust gas,
Calculating the superficial velocity of the fluidized incinerator based on the calculated or measured amount of exhaust gas,
A method for reducing N ₂ O emissions in exhaust gas, the method comprising controlling the superficial velocity by adjusting the pressure of compressed air supplied from a supercharger. The superficial velocity is compared with the set minimum value, and if the superficial velocity is below the minimum value, the opening degree of the control valve in the exhaust gas bypass path of the turbocharger is increased to reduce the amount of exhaust gas sent to the turbocharger. to reduce the rotational speed of the supercharger and reduce 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 amount of exhaust gas sent to the turbocharger. in the exhaust gas according to claim 1, characterized in that the rotation speed of the supercharger is increased by increasing the opening degree of the surplus air control valve, and the pressure after the supply path is maintained. A method for reducing N ₂ O emissions. Claim 1 or Claim 2, characterized in that the superficial velocity is controlled to such a value that the discrepancy is 0 or less in the relationship between the superficial velocity and the discrepancy between the correlation formula calculated N ₂ O and the measured N ₂ O value. The method for reducing N ₂ O emissions in exhaust gas described above. 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:
Calculating the amount of exhaust gas discharged from the fluidized incinerator based on the gas generated in the fluidized incinerator, or directly measuring the amount of exhaust gas,
Calculating the superficial velocity of the fluidized incinerator based on the calculated or measured amount of exhaust gas,
A control device that operates based on a control program for reducing the amount of N ₂ O emissions in exhaust gas, characterized in that the pressure of compressed air supplied from a supercharger is adjusted to control the superficial velocity. The superficial velocity is compared with the set minimum value, and if the superficial velocity is below the minimum value, the opening degree of the control valve in the exhaust gas bypass path of the turbocharger is increased to reduce the amount of exhaust gas sent to the turbocharger. to reduce the rotational speed of the supercharger and reduce 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 amount of exhaust gas sent to the turbocharger. 5. The control device according to claim 4, wherein the control device increases the rotational speed of the supercharger by increasing the number of revolutions of the supercharger, and also increases the opening degree of the surplus air control valve to maintain the pressure after the supply path. . Claim 4 or Claim 5, characterized in that the superficial velocity is controlled to such a value that the discrepancy is 0 or less in the relationship between the superficial velocity and the discrepancy between the correlation formula calculated N ₂ O and the measured N ₂ O value. Control device as described.

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