JP4921009B2 - Circulating fluid furnace - Google Patents

Description

  The present invention relates to a circulating fluidized furnace capable of enhancing the agitation / mixing property in the radial direction of a fluidized bed so that the object to be treated can be completely combusted even if it is sludge having a high water content.

  Conventionally, as a facility for burning industrial waste, municipal waste, sewage sludge and the like, a circulating fluidized furnace as shown in Patent Document 1 and Patent Document 2 has been widely used. This circulating fluidized furnace consists of a riser, which is a cylindrical furnace body, a high-temperature cyclone, and a downcomer for returning the fluidized medium. Combustion air is sent into the furnace through a dispersion pipe at the bottom of the fluidized bed. At the same time as the silica sand is fluidized, the fluid medium (silica sand) that is supplied to the fluidized bed, such as sludge cake, is dried and burned in a short time, and discharged from the top of the riser to the outside of the furnace. This system separates the combustion gas and incinerated ash by a cyclone and then circulates it down the furnace through a downcomer.

This circulating fluidized furnace has a gas flow rate in the riser as high as about 4 to 6 m / sec and is very excellent in the vertical stirrability but poor in the radial stirrability. When incineration of sludge with a high moisture content and large moisture fluctuation, or residue mixed fired products, it is difficult to completely burn, and as a result, the concentration of unburned gas at the outlet of the circulating fluidized furnace increases. there were. In addition, the upper part of the riser and the cyclone are burned while mixing the material to be treated, unburned gas, and fluidized medium. However, the limit of the residence time in the furnace is about 2 to 3 seconds due to restrictions on equipment arrangements. However, there is a problem that it is difficult to complete the combustion because the residence time is short as compared with the bubble flow furnace.
On the other hand, since the blower for flowing the fluidized medium requires a large amount of power, it can be considered that the combustion air is divided into the primary air for fluidizing medium flow and the secondary air for combustion, and individual blowers are used respectively. There are problems such as the size of the heat exchanger installed in the subsequent stage of the circulating fluidized furnace being severe and the need to install a separate cooling fan. Met.
JP 2005-299938 A JP 2004-69189 A

The present invention solves the above-mentioned problems and enhances the agitation / mixability in the radial direction of the fluidized bed. in which the completed main purpose is to provide a circulating fluidized furnace where Ru can be. The present invention has also been completed for the purpose of providing a circulating flow furnace that can be designed compactly without requiring a large heat exchanger or another cooling device .

Circulating fluidized bed incinerator of the present invention has been made to solve the above problems, a cylindrical riser, hot cyclones, consists downcomer for returning fluidized medium, the fluid medium to be treated by the primary air supplied from the riser bottom A circulating fluidized furnace that is mixed and fluidized to form a fluidized bed for combusting , and secondary air for agitating and mixing the object to be treated and the fluidized medium toward the concentrated portion of the fluidized bed. , A secondary air supply nozzle that is supplied obliquely downward at a flow rate of 20 to 60 m / second is provided, and tertiary air for agitating and mixing the object to be processed and the fluid medium toward the lean portion of the fluidized bed, The flow rate is 60 to 100 m / sec, and a tertiary air supply nozzle for supplying in the horizontal direction is provided .

Further, a post-combustion chamber is provided in the subsequent stage of the circulating fluidized furnace to complete combustion of the unburned portion. The invention according to claim 2 is used , and the temperature of the gas to be treated is increased at the top of the post-combustion chamber. The invention according to claim 3 is provided with a burner for holding.
Furthermore, a two-column heat exchanger comprising a first heat exchanger that recovers heat of the secondary and tertiary air and a second heat exchanger that recovers heat of the primary air is provided after the circulating fluidized furnace. and the invention according to claim 4 those were the first heat exchanger, and the invention according to what is a heat exchanger of the U tube type in claim 5.

  In the present invention, the secondary air supply nozzle for supplying the secondary air for stirring and mixing the fluidized medium toward the dense part of the fluidized bed is provided obliquely downward. The combustion efficiency can be improved.

Also, when a tertiary air supply nozzle that supplies tertiary air in a direction crossing the secondary air toward the lean part of the fluidized bed is provided, the tertiary air intersects and exhibits the screen effect, so that Stirring and mixing in the direction will be improved.
In addition, when a post-combustion chamber is provided at the subsequent stage of the circulating fluidized furnace for complete combustion of the unburned portion, a residence time of about 4 to 6 seconds can be secured as a whole. In addition, when a burner for maintaining the temperature of the gas to be processed at a high temperature is provided at the top of the post-combustion chamber, the effect is greater.
Further, a two-column heat exchanger comprising a first heat exchanger that recovers heat of secondary and tertiary air and a second heat exchanger that recovers heat of primary air is provided at the rear stage of the fluidized furnace. In this case, when the first heat exchanger is a U-tube heat exchanger, high-temperature air can be recovered with a compact and simple equipment flow.

Hereinafter, preferred embodiments of the present invention will be described with reference to the drawings.
FIG. 1 is an overall view of an apparatus showing a circulating flow furnace of the present invention. In the figure, 1 is a cylindrical riser that is a furnace body, 2 is a high-temperature cyclone, 3 is a downcomer for returning the medium, and the primary air supplied from the bottom of the riser is used for industrial waste, municipal waste, sewage sludge, etc. It is basically the same as the conventional circulating fluidized furnace in that the fluidized bed 4 is formed by mixing and fluidizing the workpiece with a fluid medium (silica sand).

  In the present invention, secondary air for agitating and mixing the fluidized medium is supplied obliquely downward (in the illustrated case, inclined by about 20 ° with respect to the axial direction of the furnace) toward the concentrated portion of the fluidized bed 4. The secondary air supply nozzle 5a is provided.

This secondary air is blown toward a dense portion such as a portion directly above the level surface where the fluidized medium of the fluidized bed 4 is stationary. The flow rate of air is about 20 to 60 m / second, and the blowing direction is as shown in FIG. As shown in FIG. 2, it is preferable to supply from four directions equally divided.
Further, the ratio of primary air for fluid medium flow to the secondary air and the tertiary air described below is basically primary air: secondary / tertiary air = 6: 4, and primary air: secondary corresponding to the object to be treated. Air can be arbitrarily adjusted in the range of 7: 3 to 5: 5.

Further, in addition to the blowing of the secondary air, if the tertiary air is supplied to the dilute portion of the fluidized bed 4 in the direction of the opposed lattice, separately from the secondary air, the exhaust gas (combustion gas by the primary air) and the tertiary Since the air intersects and exhibits a screen effect, stirring and mixing can be further promoted.
The tertiary air supply nozzle 5b is in a state in which it is horizontal in an upper part, a middle part, a lower part, or any two or more parts in a region 2 to 5 m above the level surface where the fluid medium of the fluidized bed 4 is stationary. Can be provided.

The flow rate of the tertiary air is about 60 to 100 m / second, and the blowing direction can be supplied in a direction perpendicular to the middle part and the upper part in a direction perpendicular to the middle part, for example, as shown in FIGS. .
The gas flow rate in the riser is about 5 m / second, and the mass ratio of the exhaust gas from the rich portion (combustion gas by primary air) and the secondary air + tertiary air is about 75:25.

Further, a post-combustion chamber 6 is provided at the rear stage of the circulating fluidized furnace 1 for the purpose of completing the combustion. As a result, the gas flow rate was as fast as about 4 to 6 m / sec and the residence time was as short as about 2 to 3 seconds. As a whole, the residence time was secured about 4 to 6 seconds, and complete combustion was not attempted. The generation of fuel can be prevented.
Furthermore, it is preferable to provide a burner 7 for maintaining the temperature of the gas to be processed at a high temperature at the top of the post-combustion chamber 6, whereby the exhaust gas temperature can be maintained at a high temperature of 850 ° C. or higher.
The post-combustion chamber 6 preferably has a refractory lining structure so as to withstand high temperatures, and the burner 7 is introduced in a tangential direction so that the flame of the burner 7 does not directly contact the exhaust gas, and the burner is used to prevent clinker. It is preferable to attach 7 in a reserved position.

In the latter stage of the fluidized furnace, there is a two-column heat exchanger comprising a first heat exchanger 8a that recovers heat of secondary and tertiary air and a second heat exchanger 8b that recovers heat of primary air. Is provided.
This heat exchanger uses the heat recovered from the exhaust gas to raise the temperature of the primary air and secondary / tertiary air. Using the heat recovered from the exhaust gas, to the temperature above each 650 ° C. The primary air and secondary-tertiary air in a separate heat exchanger, a small amount of air by the first heat exchanger 8a above two The secondary air and tertiary air are heated. The exhaust gas temperature at the outlet of the first heat exchanger 8a is set to 700 ° C. or higher, and the primary air can be raised to 650 ° C. also in the second heat exchanger 8b in the subsequent stage. The second heat exchanger 8b has an exhaust gas temperature of about 700 ° C. at the inlet and about 500 ° C. or more at the outlet.

In addition, it is preferable that the 1st heat exchanger 8a is a U tube type heat exchanger. In the case of a shell-and-tube heat exchanger, there is a problem with the heat resistance of the tube sheet that suspends the tube in this high temperature range, an increase in the size of the heat exchanger, and the addition of a cooler for cooling the tube sheet. Therefore, it is preferable to use a U-tube heat exchanger in which the tube can freely expand and contract and does not have a tube sheet.
By adopting such a two-column heat exchanger, it is possible to raise the temperature of primary air and secondary / tertiary air to 650 ° C or higher using heat recovered from exhaust gas with a compact and simple equipment flow. It is said.

As is clear from the above description, the present invention uses the secondary air and the tertiary air collected at 650 ° C. or higher and supplies the secondary air to the riser obliquely downward by the secondary air supply nozzle. Since the nozzle is supplied horizontally into the riser, the exhaust gas is uniformly agitated and mixed to improve contact with the fluid medium and promote combustion.

[Confirmation of effects of introducing secondary air]
FIG. 6 shows the result of evaluating the mixing state of the exhaust gas from the lower part of the fluidized bed and the secondary air and the tertiary air by the standard deviation of the riser expanded section by simulation.
From this result, it is more effective to combine with tertiary air than secondary air only (25 m / s), and even if the blowing flow rate is slow (30 m / s), stirring and mixing properties are improved. I found it bad. In addition, FIG. 7 shows that the effect of stirring and mixing is higher when the blowing locations are two stages and the blowing velocity is increased (secondary air is about 30 m / s, tertiary air is about 100 m / s).

[Confirmation of effect of extended residence time]
FIG. 8 shows the result of investigating the relationship between the residence time and the cyan density when a post-combustion chamber is installed to achieve complete combustion.

1 is an overall view of an apparatus showing an embodiment of the present invention. It is a top view explaining supply of secondary air. It is a top view explaining supply of tertiary air. It is a top view explaining supply of tertiary air. It is a top view explaining supply of tertiary air. It is a graph which shows the standard deviation by a simulation result. It is a graph which shows the standard deviation by a simulation result. It is a graph which shows the relationship between a residence time and cyan density | concentration.

DESCRIPTION OF SYMBOLS 1 Riser 2 High temperature cyclone 3 Downcomer 4 Fluidized bed 5a Secondary air supply nozzle 5b Tertiary air supply nozzle 6 Post combustion chamber 7 Burner 8a 1st heat exchanger 8b 2nd heat exchanger

Claims (5)

Cylindrical riser, hot cyclones, consists downcomer for returning fluidized medium, the object to be treated circulating and to form a fluidized bed of the combustion by mixing flow and flow medium flowing through the primary air supplied from the riser bottom A furnace ,
A secondary air supply nozzle that supplies secondary air for stirring and mixing the object to be processed and the fluid medium obliquely downward at a flow rate of 20 to 60 m / sec toward the concentrated portion of the fluidized bed is provided.
A tertiary air supply nozzle for supplying the tertiary air for stirring and mixing the object to be processed and the fluid medium in the horizontal direction at a flow rate of 60 to 100 m / second is provided toward the lean portion of the fluidized bed. Circulating flow furnace characterized by 2. The circulating fluidized furnace according to claim 1 , wherein a post-combustion chamber is provided at a subsequent stage of the circulating fluidized furnace so as to achieve complete combustion of the unburned portion. The circulating fluidized furnace according to claim 2 , wherein a burner for maintaining the temperature of the gas to be treated at a high temperature is provided at the top of the post-combustion chamber. A two-column heat exchanger comprising a first heat exchanger that recovers heat of secondary air and tertiary air and a second heat exchanger that recovers heat of primary air is provided at the subsequent stage of the circulating fluidized furnace. The circulating fluidized furnace according to any one of claims 1 to 3 , wherein The circulating fluidized furnace according to claim 4 , wherein the first heat exchanger is a U-tube heat exchanger.

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