JP4038439B2 - Operation method of circulating fluidized bed furnace - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a method for operating a circulating fluidized bed furnace for incinerating a workpiece.
[0002]
[Prior art]
Conventionally, a circulating fluidized bed furnace is known as a combustion furnace for burning an object to be treated such as sewage sludge. In a circulating fluidized bed furnace, the fluidized medium is fluidized or scattered by the fluidized air in the furnace body. At this time, the object to be treated is stirred, dried and burned, and the fluidized medium such as a cyclone connected to the furnace outlet is recovered. The fluid medium scattered by the apparatus is returned to the furnace. In such a circulating fluidized bed furnace, silica sand having an average particle size of about 300 μm, which is referred to as silica sand No. 6, and silica sand having an average particle size of about 130 μm, which is referred to as silica sand No. 7, is used as a fluid medium. By using such a fluidized medium, the fluidized medium is efficiently scattered in the furnace body by the fluidized air, and is suitably collected and circulated by a cyclone or the like, so that the object to be treated is suitably stirred, dried and burned. It is.
[Patent Document 1]
Japanese Patent Laid-Open No. 2002-147725
[Problems to be solved by the invention]
However, in such a circulating fluidized bed furnace, there is a desire to burn the workpiece more efficiently.
[0004]
This invention is made | formed in view of the said subject, and it aims at providing the operating method of the circulating fluidized bed furnace which can burn a to-be-processed object efficiently.
[0005]
[Means for Solving the Problems]
The operation method of the circulating fluidized bed furnace according to the present invention is to supply fluidized air to the fluidized medium in the furnace body, separate the fluidized medium from the exhaust gas discharged from the furnace body, and return it to the furnace body. In the operation method of the circulating fluidized bed furnace in which the object to be processed is introduced into the main body and the object to be processed is combusted in the furnace body, the first powder having the first average particle diameter, and the first average particle diameter The second powder having a larger second average particle size is mixed to obtain a fluid medium, wherein the first powder is silica sand and the second powder is silica sand and limestone .
[0006]
According to the operation method of the present invention, by setting the air amount and air pressure of the fluidized air to a desired optimum value, the second powder having a large average particle size is bubble-fluidized at the lower part of the furnace body, and the dense layer Is formed. For this reason, stirring, drying, combustion, etc. of the to-be-processed object put in are performed favorably in the concentrated layer at the bottom of the furnace body. On the other hand, the first powder having a small average particle diameter is suitably scattered upward in the furnace body by the fluidized air without staying at the lower part of the furnace body, and is higher than the dense layer in the furnace body. A dilute layer in which particles are present at a predetermined concentration is formed on the free board. For this reason, the temperature of the free board is maintained at a sufficiently high temperature, and the fine solid combustible particles and the combustible gas formed by drying and combustion in the rich layer are sufficiently burned in the free board in the furnace body. For this reason, the combustion efficiency of a circulating fluidized bed furnace becomes high.
[0007]
Here, quartz sand and limestone can be illustrated as each powder.
[0008]
The first powder and the second powder are silica sand, the average particle diameter of the first powder is 0.05 mm to 0.6 mm, and the average particle diameter of the second powder is 0.2 mm or more. It is preferable that it is -0.9 mm or less.
[0009]
When a silica sand powder of about 0.2 to 0.9 mm is used as the second powder, a thick layer can be easily formed in the furnace body by this powder. Moreover, when the powder of silica sand of about 0.05 to 0.6 mm is used as the first powder, this powder can be suitably scattered in the furnace main body and the small amount discharged from the furnace main body. The powder can be suitably recovered with a cyclone or the like and circulated to the furnace body.
[0010]
Moreover, when the weight of the first powder is 1, it is preferable that the weight of the second powder is 0.5 to 2.0.
[0011]
According to this, the rich layer and the lean layer are formed in the furnace body in a well-balanced manner, and combustion is suitably performed.
[0012]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, preferred embodiments of a method for operating a circulating fluidized bed furnace according to the present invention will be described in detail with reference to the accompanying drawings. In the description of the drawings, the same or corresponding elements are denoted by the same reference numerals, and redundant description is omitted.
[0013]
FIG. 1 is a schematic configuration diagram showing a circulating fluidized bed furnace 100 in which the present embodiment is implemented.
[0014]
The circulating fluidized bed furnace 100 of the present embodiment is a furnace that incinerates an object to be treated such as sewage sludge, and a vertical cylindrical furnace body 1 in which the fluidized medium 24 is fluidized and the object to be treated is burned. The cyclone 2 that recovers particles such as the fluid medium 24 from the combustion exhaust gas discharged from the upper part of the furnace body 1 and the loop seal 3 that returns the particles such as the fluid medium 24 recovered by the cyclone 2 to the lower part of the furnace body 1 And mainly.
[0015]
At the bottom of the furnace body 1, fluidized air supplied via the fluidized air line L4 is introduced into the furnace body 1 to fluidize the fluid medium 24 and to burn the workpiece. 10, a non-combustible material or the like is extracted from the bottom of the furnace body 1 and discharged to the outside via a line L 7, and auxiliary fuel supplied via the auxiliary fuel line L 2 is burned to assist the object to be processed. An auxiliary combustion burner 13 for burning is installed.
[0016]
In addition, at the lower part of the side surface of the furnace body 1, a screw conveyor 14 for feeding a workpiece supplied through the workpiece line L1 into the furnace body 1 and secondary air supplied from the secondary air line L5. Is introduced into the center of the furnace body 1 to burn the secondary air nozzle 11 for causing secondary combustion in the furnace and the temperature raising fuel supplied via the temperature raising fuel line L3. A temperature raising burner 12 that raises the temperature of the fluid medium 24 at the time of startup or the like is installed.
[0017]
The cyclone 2 is connected to an outlet formed in the upper part of the furnace body 1, and introduces a high temperature gas containing the fluid medium 24 and the like from the outlet and turns it, so that the solid component and the gas such as the fluid medium 24 are subjected to centrifugal force. Separate with. The separated combustion exhaust gas is discharged to the subsequent stage through the exhaust gas line L6, while the recovered solid content is introduced into the loop seal 3 installed below the cyclone 2, and the loop seal 3 uses the solid content in the furnace. Circulate to the bottom of the body 1.
[0018]
Next, an operation method of the circulating fluidized bed furnace 100 according to the present embodiment will be described.
[0019]
First, a fluid medium 24 such as dredged sand is introduced into the furnace body 1 of the circulating fluidized bed furnace 100. In the present embodiment, in particular, a large particle size powder (second powder) 22 and a small particle size powder (first powder) 20 having an average particle size smaller than that of the large particle size powder 22 are: It mixes and introduce | transduces in the furnace main body 1, and it is set as the fluidized medium 24. FIG. In the present embodiment, the average particle diameter is a 50% diameter in a weight-based particle size distribution.
[0020]
Next, the fluid medium 24 is heated by the temperature raising burner 12 to a predetermined temperature, for example, 650 ° C., and primary air is introduced through the primary air nozzle 10 to fluidize the fluid medium 24. At this time, by appropriately adjusting the flow rate of the primary air, the large particle size powder 22 stays at the bottom of the furnace body 1 and is bubble-fluidized to form the dense layer 32, while the small particle size powder 20. Since the particle size is smaller than that of the large particle size powder 22, it is entrained and scattered by the gas rising in the furnace body 1, and particles are present at a predetermined concentration in the center and upper freeboards of the furnace body 1. A lean layer 30 is formed. The gas discharged from the inside of the furnace body 1 is introduced into the cyclone 2, and the fluid medium 24 mainly composed of the small particle size powder 20 is recovered by centrifugal force and recovered to the bottom of the furnace body 1 via the loop seal 3. On the other hand, the gas from which the fluid medium 24 mainly including the small particle size powder 20 is removed is discharged to the outside.
[0021]
Next, an object to be processed is introduced into the furnace body 1 via the screw conveyor 14 and further secondary air is supplied to the free board. As a result, the object to be processed is held and fluidized in the dense layer 32 which has been heated to about 650 ° C. by the temperature raising burner 12, and the object to be processed is stirred and dried, and further combusted. In addition, unburned gas such as CO and H ₂ generated by such combustion, minute combustible particles, and the like rise together with the small particle size powder 20 forming the thin layer 30 in the free board, It is combusted by the secondary air supplied to it. At this time, since the dilute layer 30 having a sufficient particle concentration is formed by the small particle size powder 20 in the free board, the temperature in the dilute layer 30 is maintained at about 850 ° C., thereby raising the free board. Primary combustion gas and solid content are burned sufficiently.
[0022]
In the above-described combustion process, heating can be performed by the auxiliary burner 13 so that the dense layer 32 can maintain a predetermined temperature as necessary.
[0023]
Here, a silica sand powder having an average particle size in the range of 0.2 to 0.9 mm is used as the large particle size powder 22, and an average particle size is 0.05 to 0 as the small particle size powder 20. It is preferable to use silica sand powder within a range of .6 mm.
[0024]
When such a large particle size powder 22 is used, a dense layer 32 that is sufficiently bubble-fluidized can be suitably formed in the furnace body 1, and the object to be treated can be sufficiently retained to be stirred, dried, and burned. Preferably done. When the average particle size of the large particle size powder 22 is smaller than 0.2 mm, the formation of the dense layer 32 tends to be difficult. On the other hand, when the average particle size is larger than 0.9 mm, sufficient bubbles in the dense layer 32 are obtained. It tends to be difficult to fluidize.
[0025]
Further, when the small particle size powder 20 as described above is used, the diluted layer 30 having a sufficient concentration can be easily formed on the free board above the concentrated layer 32. When the average particle size of the small particle size powder 20 is smaller than 0.05 mm, it tends to be difficult to collect the small particle size powder 20 in the latter cyclone 2, while the average particle size is 0.6 mm. When exceeding, it tends to become difficult to disperse by the fluidized air in the furnace body 1.
[0026]
In addition, when the input weight of the large particle size powder 22 is WL and the input weight of the small particle size powder 20 is WS, each of them is set to satisfy 0.5 ≦ (WS / WL) ≦ 2.0. It is preferable to determine the input weight.
[0027]
In this way, the large particle size powder 22 and the small particle size powder 20 are present in a weight ratio of at least 1/3 or more, and the dense layer 32 and the dilute layer 30 are formed in the furnace body 1 in a well-balanced manner. Is done. For this reason, stirring, drying, and combustion of the workpiece are performed more efficiently.
[0028]
When the weight ratio is out of this range, the large particle size powder 22 decreases and the dense layer 32 becomes insufficient in height, or the small particle size powder 20 decreases and the concentration of the diluted layer 30 is sufficient. There is a tendency to disappear.
[0029]
Here, the total amount (WL + WS) of the fluid medium to be input depends on the moisture load of the workpiece to be burned more efficiently based on the capacity of (furnace bottom area) × (height 1 m) in a stopped state. It is preferable to set.
[0030]
The weight WL of the large particle size powder 22 is based on ensuring that the total height of the thick layer 32 is about 1.5 m or more, and the bubbling of the thick layer 32 is performed while the workpiece is sufficiently held. In order to carry out, it is preferable to set based on the relationship between the bulk specific gravity of the workpiece and the bulk specific gravity of the large particle size powder 22.
[0031]
Moreover, as the large particle size powder 22 or the small particle size powder 20, for example, silica sand or limestone can be suitably used. In addition, when limestone is used, neutralization of acidic gases, such as sulfur oxide gas in combustion exhaust gas, chlorine-type gas, such as dioxin, and cyanide-type gas, can be performed simultaneously. Further, limestone or silica sand may be mixed and used as the large particle size powder 22 or the small particle size powder 20.
[0032]
If the particle size of the large particle size powder 22 or the small particle size powder 20 becomes small due to wear, deterioration due to high temperature, or the like due to long-time operation, each fluid medium should be replenished periodically. If this is the case, suitable combustion can be continued.
[0033]
As described above, in the operation method of the circulating fluidized bed furnace according to the present embodiment, the large particle size powder 22 and the small particle size powder 20 having an average particle size smaller than this are mixed and fluidized. The medium 24 is used. For this reason, the large particle size powder 22 is bubble-fluidized in the lower part of the furnace body 1 to form a thick layer 32, and stirring, drying and combustion of the workpiece to be processed are performed in the thick layer 32 at the lower part of the furnace body 1. Done well. On the other hand, the small particle size powder 20 is suitably scattered in the furnace body 1 by the fluidized air, and the diluted layer 30 in which particles are present at a predetermined concentration is present on the free board above the dense layer 32 in the furnace body. It is formed. For this reason, the temperature of the free board is maintained at a sufficiently high temperature, and a minute solid combustible component or combustible gas is sufficiently burned in the free board in the furnace body 1. As a result, the combustion efficiency of the circulating fluidized bed furnace 100 is increased, the amount of air and auxiliary fuel can be reduced, and stable operation is possible.
[0034]
Next, examples according to the present embodiment will be described.
[0035]
In this example, silica sand No. 5 powder was used as the large particle size powder 22, and silica sand No. 6 powder was used as the small particle size powder 20.
[0036]
The powder of silica sand No. 5 is silica sand having a particle size distribution of 0.2 to 0.8 mm as shown by line B in FIG. 2, and as shown in FIG. 3, the average particle size is 580 μm and the bulk specific gravity is 1 .32 g / cm ³ , the true specific gravity is 2.56 g / cm ³ , and the loss on ignition is 0.31%. Here, in this example, the average particle diameter is a 50% diameter in a weight-based particle size distribution.
[0037]
The silica sand No. 6 powder is silica sand having a particle size range of 0.1 to 0.4 mm as shown by line C in FIG. 2, and has an average particle size of 300 μm and a bulk specific gravity as shown in FIG. Is 1.24 g / cm ³ , the true specific gravity is 2.56 g / cm ³ , and the loss on ignition is 0.31%.
[0038]
The input weight WL of the large particle size powder 22 and the input weight WS of the small particle size powder 20 were set to be WS / WL = 0.5.
[0039]
And it operated as mentioned above and supplied the sewage sludge as a to-be-processed object, and combusted. Here, the bulk specific gravity of the dehydrated sludge having a moisture content of 82% was 0.83.
[0040]
As a result, it is confirmed that a thick layer 32 having a sufficient height is formed at the bottom of the furnace body 1 and a diluted layer 30 having a sufficient concentration is formed in the free board portion, so that sewage sludge is efficiently burned. It was. In addition, the average particle diameter and ignition loss of the obtained CFB ash are shown in the line F of FIG. 2 and FIG.
[0041]
In addition, when the powder of silica sand No. 5 is used as the large particle size powder and the powder of silica sand No. 7 shown in FIG. When the silica sand No. 4 powder shown in FIG. 3 is used and the silica sand No. 5 powder is used as the small particle size powder, the silica sand No. 4 powder is used as the large particle size powder. When silica sand No. 6 powder is used as the diameter powder, when silica sand No. 4 powder is used as the large particle diameter powder and silica sand No. 7 powder is used as the small particle diameter powder, large particle diameter powder is used. Experiments were also conducted in the case of using silica sand No. 6 powder as the body and silica sand No. 7 powder as the small particle size powder, and similar results were obtained.
[0042]
Furthermore, the same result was obtained even when limestone was used as the fluid medium, and limestone having a large particle diameter of 1 mm and a small particle diameter having an average particle diameter of 0.03 mm were used.
[0043]
【The invention's effect】
According to the operation method of the circulating fluidized bed furnace according to the present invention, the first powder having the first average particle diameter is mixed with the second powder having the average particle diameter larger than the first average particle diameter. The medium. Then, the second powder is fluidized in the lower part of the furnace body with fluidized air to form a thick layer, and the agitated / dried or burned of the workpiece to be processed can be satisfactorily performed in the thick layer at the bottom of the furnace body. Let it be done. Also, the first powder is scattered upward in the furnace body with fluidized air, the freeboard temperature is maintained at a sufficiently high temperature, and the formed fine solid particles and combustible gas are sufficiently burned in the freeboard. . This provides a method for operating a circulating fluidized bed furnace capable of efficiently burning a workpiece.
[Brief description of the drawings]
FIG. 1 is a schematic configuration diagram showing a circulating fluidized bed furnace according to the present embodiment.
FIG. 2 is a diagram showing a particle size distribution of powder used in the present embodiment.
FIG. 3 is a diagram showing characteristics of powder used in the present embodiment.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 ... Furnace body, 24 ... Fluid medium, 20 ... Small particle size powder (first powder), 22 ... Large particle size powder (second powder), 2 ... Cyclone, 3 ... Loop seal, 100 ... Circulation Fluidized bed furnace.

Claims (3)

In the furnace body, fluidized air is supplied to the fluid medium, the fluid medium is separated from the exhaust gas discharged from the furnace body, returned to the furnace body, and an object to be treated is introduced into the furnace body. In the operation method of the circulating fluidized bed furnace in which the object to be treated is combusted in the furnace body,
Mixing a first powder having a first average particle size and a second powder having a second average particle size larger than the first average particle size, the fluid medium ,
The method of operating a circulating fluidized bed furnace, wherein the first powder is silica sand and the second powder is silica sand and limestone . The average particle diameter of the silica sand of the first powder is 0.05 mm to 0.6 mm, and the average particle diameter of the silica sand of the second powder is 0.2 mm to 0.9 mm. The operation method of the circulating fluidized bed furnace according to claim 1. The circulating fluidized bed according to claim 1 or 2 , wherein the weight of the second powder is 0.5 to 2.0 when the weight of the first powder is 1. How to operate the furnace.

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