JP3172751B2 - Fluidized bed combustion method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a fluidized bed combustion method in which refuse such as municipal waste and industrial waste is fluidized and burned by a fluidized bed.

[0002]

2. Description of the Related Art Generally, a stoker type furnace and a fluidized bed furnace have been widely used for incineration of refuse such as municipal refuse and industrial waste. Each of these furnaces has its advantages and disadvantages, and a good comparison is made.

For example, a fluidized bed furnace is superior to a stoker furnace in the following points. Waste plastic or garbage containing a large amount of plastic cannot be fired in a stoker furnace, but can be fired without problems in a fluidized bed furnace. Because the waste plastic melts when heated, the molten plastic in the stoker furnace may leak downward from the air holes of the grate and ignite in the lower hopper. Therefore, garbage with a high plastic content is unsuitable for stoker furnaces and has a plastic content of about 20%.
Limited to: Further, when plastic is incinerated, the ash content is reduced due to the large amount of volatile components, and the grate is exposed in the furnace and cannot be protected by ash. Of course, because of the high calorie, there is burning of the grate. In a fluidized bed furnace, on the other hand, there is no need to worry. Regarding the special combustion of sludge or mixed combustion with high-calorie refuse, there are cases where the sludge is incinerated in a stoker furnace. In this case, first, the sludge is dried using a special dryer so that the water content is 50% or less. This is supplied to the drying area of the stoker, dried, and then burned. This is because the drying efficiency is low because the stoker is surface dried. On the other hand, fluidized-bed furnaces have a very high drying efficiency because of the heat storage effect of high-temperature sand and the three-dimensional combustion of flowing fluid.
Even sludge with a water content of 65% is directly injected and burned,
By co-firing with high-calorie refuse and oil combustion, even higher-moisture garbage can be burned. A fluidized bed furnace has no moving parts inside the furnace like a stoker furnace, has a simple structure, and has no consumable parts such as a grate. Fluidized bed furnaces have less burning loss of ash than stoker furnaces, almost zero. Fluid bed furnaces store high-temperature sand in the furnace,
The furnace can be started and stopped in a short time, and the operation is simple and easy. On the other hand, in the case of the stoker furnace, the fire burning operation is required, and at the time of starting, the fireplace operation using oil is required, and the operation is complicated. The stoker combustion is a plane combustion, so the combustion rate is 180
２３０230 kg / m ² h. In contrast, fluidized bed combustion is a three-dimensional combustion, so the combustion rate is 450 to 500 kg /.
m ² h, so the fire floor area is about 1 /
It becomes 2. In the case of the stoker furnace, the molten aluminum leaks under the grate, and cools and solidifies, which may cause a problem. In the case of the fluidized bed furnace, however, such a problem does not occur because it is volatilized.

[0004] Thus, fluidized bed furnaces have a number of advantages over stoker furnaces. However, fluidized bed furnaces, on the other hand, also have the following problems. In a fluidized bed furnace, since the sand flows, the forced air pressure of the pushing fan is large and the required power is large. Since the fluidized bed burns violently and is completed in a short time, it tends to burn instantaneously, and as shown in the graph of FIG. 4, CO is suddenly generated, and the amount of generated CO may often exceed 2000 ppm, and may fluctuate. There are many. For this reason, dioxin is generated frequently, and is regarded as the biggest problem in sanitary disposal of garbage. In order to prevent this, it is necessary to devise so that large waste cannot be supplied as it is as in a stoker furnace, and that waste can be continuously and quantitatively supplied by a waste crusher or a feeder with a crushing function. Next, it is necessary to study a slow combustion method to avoid rapid combustion. In the case of stoker firing, garbage for about 2 hours is always on the stoker. When air is supplied, it burns, and when the amount of air is reduced, the amount of combustion decreases. That is, the combustion amount of the refuse can be easily controlled by the amount of air supplied. On the other hand, in the fluidized bed, the combustion peaks after about 8 seconds when the refuse is charged. Therefore, it is necessary to provide a fine continuous quantitative supply simultaneously with the suppression combustion. Since combustion proceeds at a high speed in the fluidized bed, when refuse is charged, a shortage of air is temporarily caused, gasification combustion occurs in the fluidized bed, and the fuel is burned by secondary air on the freeboard in the upper space. Therefore, the freeboard temperature is typically about 150 ° C. higher than the temperature in the fluidized bed. In addition, a secondary air nozzle for performing strong stirring in the free board is required. In addition, it is necessary to perform feedforward control in which primary air (flowing air) is suppressed by detecting the input of dust and secondary air is increased. Due to the nature of combustion, fly ash is large, and in a stoker furnace, it is about 15% of the total ash content, whereas in a fluidized bed furnace, it is about 60% or more. This increases the load on exhaust gas treatment equipment such as dust collectors, and is also designated as a specially controlled waste by law.Therefore, countermeasures against heavy metals by any of ash solidification, chemical treatment, acid extraction, and melting. Must be done, but disadvantageous due to the large amount. Fluidized bed furnaces require a device that pulls out sand and incombustibles from the furnace, sieves the incombustibles, and returns the sand to the furnace. In a stoker furnace, on the other hand, this is not necessary.

[0005] Among the problems of the fluidized bed furnace described above, the biggest problem of the fluidized bed furnace is the suppression of dioxin. As the means, for example, the following means are used. Continuous quantitative supply of refuse Generally, refuse is supplied by a biaxial to quadriaxial screw conveyor, but recently, a rotary disperser is further provided at a screw outlet to prevent the lump from falling. or,
In pusher supply, instead of pushing the waste with one pusher, the pusher is divided in a plane and driven sequentially in a different way to prevent the dust from falling out and a rotary scraping device at the pusher outlet Is provided. In another pusher system, there is a method in which a drum-shaped rotary roller and a movable crushing guide are provided at a pusher dropping port, and continuous quantitative supply is performed while crushing dust. Garbage supply controller When crushed garbage is fed down the chute into the furnace, it is detected by microwaves or phototubes, the amount of secondary air is increased by reducing the flow air, and the feed forward is further reduced to reduce the speed of the feeder. A controller is provided. Slow combustion of refuse In general, there are a diffuser plate type and a diffuser tube type as a method of supplying air to a fluidized bed. FIG. 5 shows a diffuser plate type, in which an air nozzle 22 a is provided in the inclined furnace bottom 22. As a slow burning method of this method, first, the place where refuse is supplied is not provided with a flowing air nozzle, it is a moving bed F ', and garbage is mixed in high-temperature sand to avoid instantaneous burning and garbage is baked. age,
Weight loss due to gasification. Next, when the refuse moves on the inclined surface and enters the fluidized bed F ″, the refuse contacts the fluidizing air A and burns violently. FIGS. 6A to 6D show a diffuser type. Unlike the conventional case, strong flow is not performed, the flow air amount A is reduced as a whole, and the flow air A is strongly ejected from only one of the plurality of air diffusers 23, and the strong air diffuser 23 is discharged. 7 (A) to 7 (C) also show a diffuser type, in which the air A for flowing is ejected from each diffuser 23.
The strength is changed, and this is changed alternately.
In FIGS. 5 to 7, reference numeral 24 denotes a furnace main body, 25 denotes a refuse inlet, 26 denotes a wind box, 27 denotes an incombustible substance outlet, and 28 denotes an exhaust gas outlet.

[0006]

However, each of these suppression combustion methods is an improvement of the existing fluid combustion, and has some effect of the suppression combustion. However, in the conventional combustion method shown in FIGS. 5 to 7, it is a fact that it is not possible to cope well when the property and the combustion state of the refuse greatly change. This is because the conventional combustion method has a relatively narrow control range because the amount of the flowing air ejected from the diffuser plate and the amount of the flowing air ejected from each diffuser tube are predetermined. It is. For this reason, when the property or combustion state of the refuse significantly changes, there is a possibility that a large amount of CO and dioxin may be generated due to a shortage of combustion air.

[0007] The present invention has been made in view of the above points, and it is an object of the present invention to provide a fluidized bed combustion method that can stably and satisfactorily burn refuse according to the properties of the refuse. It is.

[0008]

In order to achieve the above object, a fluidized bed combustion method according to the present invention is directed to a method in which fluidized air A jetted from a diffused region Z into a fluidized medium layer flows over the region Z. In a fluidized-bed combustion method in which a bed F is formed and refuse is fluidly burned by the fluidized bed F, the diffusion zone Z
From the immediate lower part of the refuse input port 11 to the incombustible discharge port 12
A plurality of diffuser area portions in parallel to the Z _1, Z _2, partition ... to
Then, the flow ejected from each of the aeration regions Z ₁ , Z ₂ ,.
Mix exhaust gas G generated in fluidized bed F with working air A
At the same time, the mixing ratio of exhaust gas G to flowing air A
Mix exhaust gas G so that it gets larger as it approaches
The basic configuration of the present invention is to control the amount to be increased or decreased according to the properties of the refuse and the combustion state.

[0009]

[0010]

According to the combustion method of the present invention, the exhaust gas is mixed with the flowing air ejected from the diffuser region to the fluidized bed, and the mixing ratio is changed according to the properties of the waste and the combustion state.
Even flammable refuse is slowly dried, thermally decomposed, and burned. Therefore, there is no temporary shortage of combustion air due to the introduction of waste.
The generation of CO and dioxin is effectively suppressed. In particular, fluidized air with a larger mixing ratio of exhaust gas is supplied to the fluidized bed portion into which the refuse is injected, and the mixing ratio of the exhaust gas is gradually reduced in other fluidized bed portions as it goes to the outlet of incombustibles. Since the air for use is supplied, the drying, thermal decomposition and combustion of the refuse are performed more stably and favorably, and the generation of CO and dioxin can be suppressed more effectively.

In the combustion method of the present invention, the O ₂ amount can be changed without changing the entire flow air amount, and the mixing ratio of the exhaust gas can be changed in the range of 0 to 100%. The control range can be widened and the control can be fine. Therefore, compared with the conventional combustion method, it is much more flexible, can cope with a wide range of refuse, and can control combustion precisely.
Regardless of the nature of the refuse, generation of CO and diokincin can be effectively suppressed.

[0012]

Embodiments of the present invention will be described below in detail with reference to the drawings. FIG. 1 is a schematic system diagram of a refuse treatment system for carrying out the method of the present invention. 1 is a fluidized bed furnace for burning refuse such as municipal waste and waste, and 2 is a high-temperature exhaust gas generated in a fluidized bed furnace 1. An air preheater for preheating the flowing air A from G, 3 is a forced air ventilator for the flowing air A, 4 is a secondary air ventilator, 5 is a water jet cooling tower for reducing the temperature of the exhaust gas G, 6 is A dust collecting device (for example, an electric dust collector, a bag filter, etc.) for collecting dust and the like in the exhaust gas G;
8 is a chimney, 9 is an exhaust gas recirculation ventilator.

As shown in FIG. 2, the fluidized-bed furnace 1 forms an air diffusion zone Z in the
Are divided into a plurality of air diffusion region portions Z _1, Z _2, ... Arranged in parallel from the immediately lower portion of the refuse inlet 11 to the incombustible material discharge port 12, and each of the air diffusion region portions Z _1, Z ₂ ,. by ejecting the fluidizing air a and exhaust gas G is respectively supplied, they each diffuser area portion Z _1, Z _2, ... from such silica sand fluidized medium layer by an air supply mechanism 13 and the exhaust gas supply mechanism 14, The fluidized bed F is formed on the diffusion region Z.

In the diffuser area Z, a diffuser plate 15 having an air nozzle 15a is provided in the furnace body 10, and a plurality of wind boxes 16a, 16b,... Are provided below the diffuser plate 15. Is formed by That is, the diffuser plate 15
As shown in FIG. 2, the furnace body 10 is disposed so as to be inclined downward from immediately below the waste inlet 11 to the incombustible discharge outlet 12, and is disposed on the diffuser plate 15. A number of air nozzles 15a are provided for ejecting a mixed fluid of the flowing air A and the exhaust gas G toward the outlet 12 side. The wind boxes 16a, 16b,... Are arranged below the diffuser plate 15 so as to be arranged in parallel in the inclination direction of the diffuser plate 15, and the wind boxes 16a, 16b,. Air nozzle 1
A mixed fluid of the flowing air A and the exhaust gas G is supplied to 5a. In the present embodiment, four wind boxes 16a, 16b, 16c, 16d are arranged below the diffuser plate 15,
Air diffusion region Z four aeration region portion _{Z 1, Z 2, Z 3} , are divided into Z _4.

As shown in FIG. 2, the air supply mechanism 13 includes an air supply pipe 17 connected to the push-in ventilator 3 and an air pipe 1 guided to each of the wind boxes 16a, 16b, 16c and 16d.
7a, 17b, 17c, and 17d are branched and connected,
A damper 18 is provided in each of the air pipes 17a, 17b, 17c, 17d.
And wind boxes 16a, 16b, 16c, 16
The amount of flow air A supplied to d is controlled so as to decrease as it approaches the inlet 11.

As shown in FIG. 2, the exhaust gas supply mechanism 14 includes an exhaust gas supply pipe 1 connected to the exhaust gas recirculation ventilator 9.
9, the gas pipe 1 led to each of the wind boxes 16a, 16b, 16c
9a, 19b, and 19c are branched and connected, and a damper 20 is interposed in each of the gas pipes 19a, 19b, and 19c.
The amount of the exhaust gas G supplied to each of the wind boxes 16a, 16b, 16c is controlled to increase as approaching the inlet 11. Therefore, the mixing ratio of the exhaust gas G with respect to the flowing air A ejected from each of the diffusion region portions Z _1, Z ₂ ,.

By the way, the flowing air A contains 21% O ₂ , and the exhaust gas G contains about 10 to 12%.
% O ₂ . Now, if it is assumed that O ₂ in the exhaust gas G is 11%, by mixing it with the flowing air A, O ₂ of the flowing air A can be freely selected from 11% to 21%. According to experiments and research conducted by the present inventors, it was found that O ₂ in the combustion air of garbage was 17%
Below this, the combustion deteriorates extremely, making it impossible to maintain continuous combustion.

Therefore, in this embodiment, the input port 11
Bed portion F ₁ corresponding to the wind box 16a closest to
Zone) is the position where the refuse is charged and is a portion where it is desired to suppress combustion, so the O ₂ amount is set to 16%. In this case, since the temperature of the sand is kept at a high temperature, gasification combustion occurs, and the refuse flows toward the discharge port 12 while being stirred because the sand is maintained in a fluid state. The fluidized bed portion F ₂ corresponding to the second wind box 16b from the charging port 11 (second zone)
Sets the O ₂ amount to 18% in consideration of slow combustion. Further, the fluidized bed portion F ₃ (third zone) corresponding to the third wind box 16c from the charging port 11 is provided with an O port in consideration of quasi-slow combustion.
_The amount of ₂ is 20%. The fluidized bed portion F ₄ (fourth zone) corresponding to the wind box 16 d closest to the discharge port 12
Has 21% O ₂ as the finishing zone for flame retardant,
Complete combustion by performing strong combustion. The mixing ratio of the fluidizing air A and the exhaust gas G in this case, the first zone F ₁ in fluidizing air A50%, exhaust gas G50%, second zone F ₂ in fluidizing air A70%, G30% gas, Zone 3 F ₃ the fluidizing air A89.5%, G10.5% gas, fourth
Zone F ₄ in fluidizing air A100%, the G0% flue gas. The total flow air A amount is about 77% and the exhaust gas G
The amount amounts to about 23%.

In the fluidized bed furnace 1 configured as described above, the refuse charged into the fluidized bed F in the furnace body 10 from the charging port 11 is composed of a flowing medium, flowing air A and exhaust gas G. The mixture is agitated by the mixed fluid, dried and burned, and the burned matter and the incombustible matter are discharged to the incombustible matter discharge port 12.

At this time, the first zone F into which refuse is thrown
_{In the case of 1} , since the amount of exhaust gas G is large and the amount of O ₂ is small, even if the refuse introduced from the inlet 11 is easily combustible, it is rapidly dried, thermally decomposed and burned. no, occurs some gasification and combustion, garbage is going to flow to the second zone F _2. Therefore, a situation in which a large amount of pyrolysis gas is not generated and combustion air is insufficient is avoided.
As a result, generation of CO and diokincin is effectively suppressed.

Further, in the second zone F ₂ and the third zone F ₃ , the amount of the exhaust gas G is gradually reduced, and the amount of O _{2 is} larger than that of the first zone F _1. In this case, drying, thermal decomposition and burning are not suddenly performed, and these are performed extremely slowly. Therefore, there is no shortage of combustion air,
The generation of CO and diokincin is effectively suppressed.

[0022] Then, in the fourth zone F _4, the exhaust gas G is not supplied, since the only fluidizing air A is supplied, the intensive combustion. Therefore, even if the refuse is inflammable, it is sufficiently dried and burned, and when the refuse reaches the discharge port 12, it is surely completely burned.

The numerical values of the flow air amount A, the exhaust gas amount G, and the O ₂ amount shown in the above embodiment are merely examples.
It can be controlled freely according to the properties of the refuse and the combustion state. In the combustion method of the present invention, the amount of O ₂ can be changed without changing the amount of the flowing air A as a whole, and the mixing ratio of the exhaust gas G can also be changed in the range of 0 to 100%. The range can be widened and the control can be fine. Therefore, compared to the conventional combustion method, it is much more flexible, can cope with a wide range of waste quality, can control combustion precisely, and can reduce CO2 regardless of the property and combustion state of the waste. And the generation of diokincin can be effectively suppressed.

It should be noted that the present invention is not limited to the above-described embodiment, and can be appropriately modified and changed without departing from the basic principle of the present invention. That is, in the above embodiment, four wind boxes 16a are arranged below the diffuser plate 15 to divide the diffusion area Z into four, but the number of the wind boxes 16a is
It can be set arbitrarily according to the area of the diffuser plate 15, the combustion conditions, and the like. For example, a wind box 16
a ... may be arranged in three or five or more.

FIG. 3 shows a case in which the method of the present invention is applied to a diffused tube type fluidized bed furnace 1. A plurality of diffuser tubes 21a, 21b, 21c, 22d are arranged in a furnace body 10 in parallel. The air diffusion zone Z is formed, and the air diffusion zone Z is defined by each of the air diffusion tubes 21a,
By changing the mixing ratio of the exhaust gas G to the flowing air A ejected from 21b, 21c, 22d, it is divided into a plurality of air diffusion regions. That is, in this embodiment, the mixing amount of the exhaust gas G is such that the mixing ratio of the exhaust gas G to the flowing air A spouted from each of the air diffusers 21a, 21b, 21c, 22d increases as approaching the inlet 11. To control. Incidentally, in FIG.
3 is an air supply mechanism and 14 is an exhaust gas supply mechanism. This diffused tube type fluidized bed furnace 1 can also provide the same operation and effects as those of the above embodiment.

In this embodiment, although not shown, the amount of CO in the exhaust gas G and the NO
The air supply mechanism and the exhaust gas supply mechanism are respectively controlled by the controller so that both the CO amount and the NOx amount in the exhaust gas are the minimum values. The mixture ratio of G may be automatically controlled to increase or decrease.

[0027]

As is clear from the above description, the present invention mixes exhaust gas with fluidizing air supplied from a diffuser region to a fluidized bed, and adjusts the mixing ratio according to the properties of the refuse and the combustion state. To change it. That is, since the amount of O ₂ is changed without changing the entire amount of the flowing air, the waste can be stably and satisfactorily burned according to the properties of the waste,
Generation of CO and dioxin can be suppressed.
Further, since the mixing ratio of the exhaust gas can be changed in the range of 0 to 100%, the control range can be widened and the control can be fine. As a result, it is possible to appropriately cope with various and various kinds of waste. Furthermore, when the diffusion region is divided into a plurality of diffusion regions and the mixing ratio of the exhaust gas to the flowing air ejected from each diffusion region is changed, combustion can be precisely controlled. The above effects can be more reliably achieved.

[Brief description of the drawings]

FIG. 1 is a schematic system diagram of a refuse disposal system that implements the method of the present invention.

FIG. 2 is a schematic sectional view showing a main part of a fluidized bed furnace of the refuse treatment system.

FIG. 3 is a schematic sectional view showing another embodiment of the fluidized bed furnace.

FIG. 4 is a graph showing the amount of CO generated in a conventional fluidized bed furnace.

FIG. 5 is a schematic sectional view of a conventional fluidized-bed furnace using a diffuser plate.

FIG. 6 is a schematic explanatory view showing a conventional fluidized bed furnace combustion method using a diffuser tube.

FIG. 7 is a schematic explanatory diagram showing a combustion method of a conventional fluidized-bed furnace using an air diffuser.

[Explanation of symbols]

A fluidized air, F is fluidized layer, G is an exhaust gas, Z is the air diffuser _{area, Z 1, Z 2, Z} 3, Z 4 is an air diffuser area portion, of the 11 Wagomi inlet, 12 of incombustible material Vent.

Continuation of the front page (51) Int.Cl. ⁷ identification code FI F23G 5/50 ZAB F23G 5/50 ZABN (58) Investigated field (Int.Cl. ⁷ , DB name) F23G 5/30 F23G 5/50 F23C 10/00

Claims (1)

(57) [Claims] 1. A fluidized bed (F) is formed on a diffused area (Z) by means of fluidized air (A) spouted into the fluidized medium layer from the diffused area (Z). garbage in fluidized bed combustion method which is adapted to flow combustion air diffuser region
(Z) from the immediate lower part of the refuse input port (11)
A plurality of diffuser zones parallel to the outlet (12)
(Z ₁ ), (Z ₂ ), ...
Flowing air ejected from (Z ₁ ), (Z ₂ ), ...
Exhaust gas (G) generated in the fluidized bed (F) is mixed with (A).
Of the exhaust gas (G) against the flowing air (A)
So that the mixing ratio increases as it approaches the inlet (11)
A fluidized bed combustion method, wherein the mixing amount of the exhaust gas (G) is controlled to increase or decrease according to the properties of the refuse and the combustion state.