JP2002039519A - External circulation type fluidized bed furnace and method for processing waste using the furnace - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve agitation effect of exhaust gas and to improve combustion, in an outside circulation type fluidized bed furnace. SOLUTION: Waste is fed in a furnace through a charge port 10 formed in the central part of the top of a furnace. A turbulent flow is generated in circulation sand and a circulation flow of exhaust gas by a free board 6. This constitution vaporizes the moisture content of waste, while exhaust gas is being agitated. Thereafter, the waste is caused to reach a concentrated layer part at the lower part of the furnace.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a fluidized bed incinerator, and more particularly to an external circulating fluidized bed used for incinerating solid carbonaceous waste such as sewage sludge, municipal waste, industrial waste, and coal. The present invention relates to a furnace and a method for treating waste using the furnace.

[0002]

2. Description of the Related Art Fluidized bed incinerators have been widely used for incineration of industrial waste, municipal waste, sewage sludge, and the like. Fluidized bed incinerators have a high heat absorption capacity in fluidized beds,
Suitable for burning high moisture content waste such as sludge.

Here, fluidized bed incinerators are classified into bubble fluidized bed furnaces and circulating fluidized bed furnaces. Among these, a bubble fluidized bed furnace is a method in which fluidized sand such as sand is laid on the hearth, and the sand is fluidized by blowing primary air to bring the inside of the bed into a boiling state, and from about 1 to 1.5 m above the fluidized bed. It is configured to throw and burn waste such as sludge.

[0004] However, in this bubble fluidized bed furnace, a part of the waste combustion is relied on the free board, and the free board tends to overheat. This is because when incinerating waste with high moisture content and high volatility such as sewage sludge, the temperature in the furnace sand layer (dense layer) evaporates the moisture in the waste, and the temperature tends to decrease. Conversely, in the freeboard portion, the combustibles gasified in the sand layer portion burn and tend to overheat, and as a result, it is necessary to increase the freeboard volume. Accordingly, a circulating fluidized bed furnace has been proposed in which the temperature difference in the furnace is small and the amount of exhaust gas can be reduced and the equipment can be made compact by circulating fluidized sand.

An example of such a circulating fluidized bed furnace will be described with reference to FIG. This circulating fluidized bed furnace includes a fluidized bed furnace main body 3 composed of a free board 1 and a fluidized bed 2, a hot cyclone 5 for collecting fluidized sand blown up to the free board 1 through an outlet duct 4, Downcomer 6 for returning liquid sand, and seal pot 7 for preventing unburned gas in the furnace from flowing into hot cyclone 5
And a return pipe 8.

In such a fluidized-bed furnace, when waste is supplied from the inlet 10 to the fluidized bed 2 fluidized by the primary air introduced from the primary air inlet 9, the waste is collected in the fluidized bed 2. While being mixed and agitated, it is made finer by contact with the liquid sand, and is burned while being dried and thermally decomposed while flowing in a mixed state with the liquid sand. On the other hand, the fluidized sand blown up from the fluidized bed 2 and the light waste such as unburned gas and volatile matter in the sludge are led to the free board 1 together with the secondary air supplied from the secondary air inlet 11, and The unburned portion is burned in the board 1. Thereafter, the fluidized sand is collected by the cyclone 5 through the outlet duct 4 and returned to the fluidized bed furnace main body 3 through the downcomer 6, the seal pot 7, and the return pipe 8.

[0007] At the upper part of the fluidized bed 2 of about 1 to 1.5 m, a waste inlet 10 is provided. The waste (especially sludge) supplied from the inlet 10 is
Moisture is evaporated in the dense bed at the lower part of the circulating fluidized bed furnace, and the volatiles are gasified and then burned. In addition,
A part of the gasified volatiles is completely burned by the agitating effect of the liquid sand in the free board 1, and the liquid sand is collected in the hot cyclone 5 and discharged out of the furnace.

However, in such a circulating fluidized-bed furnace, the residence time of the exhaust gas in the freeboard 1 is as short as 3 to 4 seconds. When incinerating waste with high volatility, there is a problem that a part of unburned gas such as CO is exhausted from the furnace without being completely burned.

[0009]

SUMMARY OF THE INVENTION The present invention has been made to solve the above-mentioned problems, and in an external circulation type fluidized furnace, waste is supplied from the center of the furnace top into the furnace. The turbulence is generated in the furnace. Here, since the waste is a solid, the kinetic energy is large and the exhaust gas, which is a gas, has a high stirring effect. In the present invention, compared to the stirring effect by secondary air blowing aimed at improving combustion,
A high exhaust gas stirring effect can be obtained.

[0010]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, an embodiment of an external circulation type fluidized bed furnace according to the present invention will be described in detail with reference to FIG. The external circulation type fluidized bed furnace shown in FIG. 1 is connected to a fluidized bed furnace main body 3 composed of a free board 1 and a fluidized bed 2 via an outlet duct 4 and an upper part of the fluidized bed furnace main body 3, A hot cyclone 5 for collecting the liquid sand blown up to the surface, a downcomer 6 for returning the liquid sand,
It comprises a seal pot 7 for preventing unburned gas from flowing into the hot cyclone 5 and a return pipe 8.
The height of the furnace is about 15 m to 20 m as measured from the primary air inlet 9.

At the center of the top of such a circulating fluidized bed furnace, a waste inlet 10 is provided. The inlet 10 is formed in a perforated plate shape as described later.

In the present embodiment, the waste is granulated in advance to, for example, about 10 mm or more. The particle size at which the waste is granulated is not limited to this, and the particle size is such that it does not fly out of the furnace as soot and causes some resistance to the flow of exhaust gas during falling in the furnace. However, in practice, it is preferable to appropriately determine the diameter in consideration of, for example, the diameter of a pipe into which the waste and the like are actually introduced into the furnace. Such granulation can be carried out by a known method using a generally known granulation material or the like. The waste thus granulated is supplied to the furnace center from the charging port 10 in the form of granules.

When such granulated waste is dropped into the furnace, the waste collides with the rising fluidized sand and the high-temperature exhaust gas, and the fluidized sand and the exhaust gas are separated in the freeboard 1. A turbulence is generated in the circulating flow to be created, and the exhaust gas is stirred. Along with this, the granular wastes reach the fluidized bed 2 after the moisture is evaporated by the circulating flow and the turbulent flow.

In the fluidized bed 2, the waste is fluidized by the primary air introduced from the primary air inlet 9, mixed and stirred, and further, is made fine by being brought into contact with the fluidized sand. Accordingly, the waste is burned while being dried and thermally decomposed while flowing in a mixed state with the fluidized sand. Here, the temperature of the primary air is preferably about 650 ° C. for the purpose of reducing auxiliary fuel in the incineration of waste having a high water content, but is not limited thereto.

Further, the unburned gas, volatile matter and light wastes in the fluidized sand and some sludge blown up in the fluidized bed 2 are transferred to the free board 1 together with the secondary air supplied from the secondary air inlet 11. The unburned portion is guided and burned in the free board 1. Thereafter, the fluidized sand is collected by the cyclone 5 through the outlet duct 4, and is passed through the downcomer 6, the seal pot 7 and the return pipe 8,
Refluxed.

FIG. 2 schematically shows the structure near the waste inlet 10. In the figure, 21 is a waste input device main body for temporarily storing waste, 22 is a perforated plate arranged at the lower part of the waste input device main body 21, and 23 is a perforated plate 22
Is a cut gate which slides on the lower surface of the opening to open and close the inlet 10, and 24 is a driving device for sliding the cut gate 23.

In the above embodiment, since waste is supplied into the furnace from the center of the furnace top to generate turbulence in the furnace, a high exhaust gas stirring effect can be obtained. For this reason, the effect of stirring the flue gas in the freeboard is also improved, and unburned gases such as CO, greenhouse gases such as N2O, and harmful gases such as DXN can be reduced.

In the above embodiment, the size of the charging port 10 is set to about 80% of the diameter of the fluidized-bed furnace body 3, for example, the furnace diameter.
Or less. Thereby, the waste can be supplied so as to be opposed to the rising flow of the fluidized sand and the exhaust gas generated in the central portion of the furnace. By supplying the waste in this way, the effect of stirring the exhaust gas can be improved.

Further, in the present embodiment, as a method of charging the waste into the furnace, for example, it is possible to granulate the waste to a size of about 10 mm or more and to uniformly input the waste from the upper part of the furnace. In this case, combustion can be improved. At the same time, the waste can be supplied at a constant particle size from the center of the top of the furnace, and turbulence can be generated uniformly with respect to the upward flow.

In this embodiment, the waste falling in the furnace collides with the rising flow of the flowing sand and the high-temperature gas as a flow facing the flow. For this reason, the moisture of the waste evaporates from the surface even during the fall.

This will be described in detail. The moisture in the waste supplied into the furnace from the top of the furnace evaporates by contact with the fluidized sand, and reaches a thick layer (also called a sand layer) at the bottom of the furnace. Since the moisture evaporates, the heat load for evaporating the waste water in the dense layer can be reduced, and the shape of the dense layer at the lower part of the furnace can be reduced in size.

Furthermore, in the present embodiment, the waste (inertial force + viscous force) acts on the waste supplied vertically below the furnace top due to the circulating flow of the fluidized sand and the exhaust gas, so that the waste is dropped freely. As compared with the case, the time to reach the dense layer portion in the lower part of the furnace can be made longer. For this reason, in addition to moisture, volatiles evaporate from the surface of the waste before reaching the dense layer at the bottom of the furnace, further reducing the heat load for water evaporation at the dense layer at the bottom of the furnace. Is done.

As described above, the time required for the waste to reach the dense layer is determined by the drag against the circulating flow acting on the waste supplied into the furnace from the top of the furnace and the gravity of the waste. This arrival time can be controlled by appropriately selecting the particle size of the waste, and can be set sufficiently large as compared with the case where the waste falls freely. Therefore, the moisture of the waste can be sufficiently evaporated during the falling time, so that the heat load required for evaporating the moisture of the waste such as sludge in the thick layer can be further reduced, and the thick layer can be reduced. Further, the furnace can be made more compact.

FIG. 4 shows an example of calculation of the particle size of waste and the like and the time required to reach the dense layer at the lower part of the furnace. As is clear from the figure, by setting the particle size of the waste and the like to 1 mm, for example, the time required to reach the dense layer portion at the lower part of the furnace is reduced.
It can be about 2.5 times longer than 10 mm. Therefore, when the particle size of the waste or the like is set to 1 mm, the water can be more effectively evaporated during the falling time of the waste or the like.

In the present embodiment, since the moisture of the waste can be sufficiently evaporated as described above, the in-layer combustion rate of the waste in the dense layer at the lower part of the furnace can be improved. In other words, since the moisture content of the waste fed into the dense bed at the lower part of the furnace is reduced, the in-bed combustion rate is improved, and most of the waste is burned in the rich bed, and The residence time is a margin. This makes it possible to reduce unburned gases such as CO, greenhouse gases such as N2O, and harmful gases such as DXN. FIG. 5 shows the relationship between the moisture load of the waste and the in-layer combustion rate as described above.

The dimensions, shapes, relative arrangements and the like of the components employed in the above embodiment are not particularly limited, and are merely examples.

[0027]

As described above, according to the external circulating fluidized bed furnace of the present invention, waste is supplied vertically downward from the center of the furnace top to generate turbulence in the furnace. Therefore, a high exhaust gas stirring effect can be obtained. This allows
It is possible to reduce unburned gases such as CO, greenhouse gases such as N2O, and harmful gases such as DXN.

Further, in the present invention, since the waste input position is located at the center of the circulating fluidized bed furnace, the waste is placed facing the upward flow of fluidized sand and exhaust gas generated at the center of the furnace. Can be supplied, whereby the effect of stirring the exhaust gas can be further enhanced.

Further, according to the present invention, waste is granulated to a certain particle size from the center of the furnace top, so that turbulent flow is generated uniformly with respect to the upward flow in the furnace. It becomes possible. Thus, even when the furnace is scaled up, it is possible to uniformly input waste at the center of the furnace, and it is possible to improve combustion.

Further, in the present invention, since the drag against the circulating flow due to the fluidized sand and the exhaust gas acts on the waste, the time required to reach the dense layer portion at the lower part of the furnace can be increased as compared with the case of free fall. it can. For this reason, it is possible to sufficiently evaporate water and volatiles from the surface of the waste before the waste reaches the dense layer portion at the lower part of the furnace.
This makes it possible to reduce the heat load required for evaporating the water content of waste such as sludge in the dense layer portion, so that the furnace shape in the dense layer portion can be reduced in size. In addition, since most of the waste is burned in the rich layer portion, the in-layer combustion rate in the rich layer portion in the lower part of the furnace can be improved, and the exhaust gas residence time in the freeboard portion can be effectively used as a margin. be able to.

In addition, according to the present invention, waste is reduced to about 1 m.
In the case where the granulated material with a diameter of m is supplied from the waste inlet, the residence time of the waste until it reaches the dense layer at the lower part of the furnace can be made sufficiently long. Thereby, the unburned gas in the exhaust gas can be more completely burned.

[Brief description of the drawings]

FIG. 1 is a view schematically showing an embodiment of an external circulating fluidized bed furnace according to the present invention.

FIG. 2 is a view schematically showing a waste (or sludge) charging device in the external circulating fluidized bed furnace shown in FIG.

FIG. 3 is a view schematically showing a conventional external circulation type fluidized bed furnace.

FIG. 4 is a diagram showing the relationship between the particle size of waste and the time required to reach a dense layer at the bottom of the furnace.

FIG. 5 is a diagram showing the relationship between the moisture load of waste and the in-layer combustion rate.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Free board 2 Fluidized bed 3 Fluidized furnace main body 4 Outlet duct 5 Hot cyclone 6 Downcomer 7 Seal pot 8 Return pipe 9 Primary air inlet 10 Waste inlet 11 Secondary air inlet 12 Burning burner 21 Waste input device body 22 Perforated Plate 23 Cut Gate 24 Drive

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat ゛ (Reference) F23G 5/44 ZAB F23C 11/02 311 (72) Inventor Toshikazu Hotta 12 Nishikicho, Naka-ku, Yokohama-shi, Yokohama, Mitsubishi Inside the Heavy Industries, Ltd.Yokohama Works (72) Inventor Shiro Sasaya 12, Nishiki-cho, Naka-ku, Yokohama-shi, Kanagawa Prefecture Inside the Mitsubishi Heavy Industries, Ltd.Yokohama Works (72) Inventor Hiroki Honda 1-8, Koura, Kanazawa-ku, Yokohama-shi, Kanagawa Prefecture Address 1 Inside the Yokohama Research Laboratory of Mitsubishi Heavy Industries, Ltd. (72) Inventor Yoshihito Shimizu 1-8-1 Koura, Kanazawa-ku, Yokohama-shi, Kanagawa Prefecture Inside the Yokohama Research Laboratory of Mitsubishi Heavy Industries, Ltd. 8th Street 1 Mitsubishi Heavy Industries, Ltd. Yokohama Research Laboratory F-term (reference) 3K064 AA10 AA17 AB03 AC01 AC05 AD0 8 AE13 BA05 BA07 BA17 3K065 AA11 AB01 AC01 AC02 AC19 BA05 CA02 CA03 EA12 EA45 EA46 4D059 AA03 BB01 BB13 BK09 BK30 EB20

Claims (5)

[Claims] 1. An external circulating fluidized-bed furnace having a fluidized-bed furnace main body, a cyclone connected to an upper part thereof, and a return pipe connecting a lower part of the cyclone and a lower part of the fluidized-bed furnace main body. An external circulating fluidized bed furnace provided at the top of a fluidized bed furnace body and generating turbulence in the furnace by supplying waste vertically downward from the waste inlet. 2. The external circulating fluidized bed furnace according to claim 1, wherein the inlet is provided substantially at the center of the top of the fluidized bed furnace body. 3. The external circulating fluidized bed furnace according to claim 2, wherein the inlet has a diameter of about 80% or less of a diameter ratio of the furnace body. 4. The external circulating fluidized bed furnace according to claim 1, wherein waste obtained by granulating waste to a diameter of about 10 mm or more is supplied from said input port. Method of treating waste using an external circulating fluidized bed furnace. 5. The external circulating fluidized bed furnace according to any one of claims 1 to 3, wherein the waste is granulated to a diameter of about 1 mm, and the time required to reach the furnace sand layer (rich layer) is reduced. Long,
A method for treating waste using an external circulating fluidized bed furnace characterized by reducing the water load on a sand layer.