JPH09210331A - Circulating fluidized bed boiler - Google Patents

Abstract

(57) [Summary] [PROBLEMS] To provide a circulating fluidized bed boiler that can reduce the generation of dioxins. SOLUTION: The waste-producing fuel is combusted in the furnace 1 while being fluidized together with the bed material 3, and the exhaust gas generated by the combustion is guided to a cyclone 4 connected to the upper part of the furnace 1 to separate the bed material 3. A circulating fluidized bed boiler configured to circulate the bed material 3 discharged by the above and separated by the cyclone 4 to the bottom of the furnace 1.
A tertiary air line 24 for introducing tertiary air (combustion air) C is provided at the inlet 4b of the fuel cell to promote combustion of unburned components in the cyclone 4 and heat a precursor of dioxin having a phenol structure remaining as unburned components. Disassemble.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a circulating fluidized bed boiler.

[0002]

2. Description of the Related Art In recent years, from the viewpoint of effective utilization of unused energy, municipal waste is crushed and calcium 10 or the like is added.
Approximately 20 mm columnar chips are solidified and dried to generate dust-producing fuel RDF (Refuse derivated fuel)
The technology for producing l) has been developed, and it has come to be considered to utilize the waste-producing fuel in a fluidized bed boiler.

FIG. 2 shows an example of a circulating fluidized bed boiler using the dust-producing fuel. An air dispersion plate 2 is provided at the bottom of a furnace 1 formed by a water cooling wall 1a.
The dust-producing fuel, which has been injected into the air dispersion plate 2 through the fuel line W, is burned by the primary air A blown from the air dispersion plate 2 while being fluidized together with the bed material 3 made of ash or limestone. The steam to be supplied to a steam turbine for power generation (not shown) is generated.

The primary air A blown out from the air dispersion plate 2 is provided with a forced draft fan (FDF) 6 and an air preheater 7 and an air line 9 connected to the lower portion of the furnace 1 through a control valve 8. Are being supplied.

Further, a cyclone 4 is connected to the upper portion of the furnace 1 so as to guide the exhaust gas generated by combustion in the furnace 1, and contains combustion ash and unburned components blown up by the exhaust gas. The bed material 3 is collected by the cyclone 4, and the bed material 3 is collected by the cyclone 4.
Is circulated from the vertical bed material falling pipe 4a below the cyclone 4 to the bottom of the furnace 1 through an ash recirculation device (J-valve or the like) 5.

Here, in consideration of the fact that the pressure in the lower part of the furnace 1 is generally higher than the pressure in the lower part of the cyclone 4, the ash recirculation device 5 takes into account the internal pressure of the furnace 1 in this state. Exhaust gas is bed material drop pipe 4 under cyclone 4
It is formed so as to prevent the bed material 3 from flowing into the a side and surely allow the bed material 3 separated by the cyclone 4 to flow down and return into the furnace 1.

On the other hand, the exhaust gas from which the bed material 3 has been separated by the cyclone 4 is subjected to heat recovery through the rear heat transfer section 18 including the superheater 16 and the economizer 17, and then flows into the exhaust gas line 19. , Is further cooled by exchanging heat with the air in the air line 9 in the air preheater 7, is dedusted by a dust collector (for example, a bag filter) 20, and is then discharged from the chimney 22 via an induction draft fan (IDF) 21. It is open to the atmosphere.

Further, the ash recirculation device 5 is adapted to be introduced with flowing air 11 from a blower 10 provided separately, and fluidizes the particles of the circulating bed material 3 to smooth the particles. To ensure the flow of.

Further, the air line 9 is also provided with a secondary air line 13 which is connected to an intermediate portion in the vertical direction of the furnace 1 through a control valve 12, and from the secondary air line 13 into the furnace 1. The secondary air B is supplied to the above to assist the combustion of unburned components.

Reference numeral 15 in the drawing denotes a bed material discharge line connected to the bottom of the furnace 1 through a cut-out valve 14 such as a rotary valve so that a part of the bed material 3 can be taken out.

[0011]

However, in such a conventional circulating fluidized bed boiler, the secondary air B introduced into the middle portion of the furnace 1 in the vertical direction is along the combustion ash blown up by the exhaust gas and the furnace wall. Since the bed material 3 or the like falling down prevents good mixing of unburned components, it is difficult to completely burn the unburned components in the furnace 1.
Even if the secondary air B is guided to the cyclone 4 and mixed well with the unburned matter due to the swirling flow, the oxygen concentration has already dropped significantly at the time when the secondary air B has flowed into the cyclone 4, and the combustion is slow. , The precursor of dioxin having a phenol structure as shown in FIG. 3 (the structural formula of chlorophenols is shown in the figure) remains as unburned content, and chlorine is supplied to this to generate dioxin (FIG. 4). However, there was a problem that polychlorinated dibenzoparadioxin of 1) or polychlorinated dibenzofuran of FIG. 5) was generated.

That is, since the garbage, which is a raw material of the waste-producing fuel, contains chlorine-based plastic, the waste-producing fuel made of the waste contains about 0.5 to 1% of chlorine. , When chlorine-containing waste-producing fuel is burned, hydrogen chloride gas is generated, and in the presence of the hydrogen chloride gas, the precursor of the dioxin having a phenol structure which remains as unburned matter is heated. The reaction produces dioxin.

In addition, the generation of dioxins accompanying the incineration of waste is contributed more by the generation in various processes (600 to 200 ° C.) in a relatively low temperature region after the furnace 1 than in the furnace 1. Is said to be large, and it is said that the production of dioxins by the catalytic reaction on the surface of fly ash particles using chlorophenol as a precursor is particularly important.

That is, almost no dioxin is produced in the gas phase, and chlorophenol adsorbed on fly ash particles and gas phase chlorophenol are produced by heterogeneous reaction using SiO ₂ on the surface of fly ash particles as a catalyst. Since the adsorption of chlorophenol to fly ash particles is likely to occur at low temperatures (desorption at high temperatures), dioxin is produced in various processes (600 to 200 ° C) in the relatively low temperature region after furnace 1. It is thought to be done.

Therefore, when the precursors of dioxin (chlorophenols) having a phenol structure remain as unburned components, the dioxin originating from the precursor is mainly generated in the equipment on the downstream side of the circulating fluidized bed boiler. It will be generated.

The present invention has been made in view of the above-mentioned circumstances, and an object thereof is to provide a circulating fluidized bed boiler capable of reducing the generation of dioxins as compared with the conventional case.

[0017]

DISCLOSURE OF THE INVENTION According to the present invention, a bed material is combusted in a furnace while fluidizing a dust-producing fuel together with the bed material, and exhaust gas generated by the combustion is guided to a cyclone connected to the upper part of the furnace. A circulating fluidized bed boiler configured to circulate the bed material separated by the cyclone to the bottom of the furnace, the air line being provided at the inlet of the cyclone. The present invention relates to a circulating fluidized bed boiler characterized by:

Therefore, according to the present invention, when the tertiary air is introduced from the tertiary air line to the inlet of the cyclone, the swirling flow generated in the cyclone causes the tertiary air and unburned components to be mixed well, and the unburned air in the cyclone is not mixed. Since the combustion of the fuel is remarkably promoted, the unburned remaining unburned in the furnace is actively burned in the cyclone and is greatly reduced.

The air line may be connected to the inlet of the cyclone via an air preheater using the exhaust gas discharged from the cyclone as a heat source.

In this way, the heat of the exhaust gas discharged from the cyclone can be effectively used to preheat the tertiary air.

[0021]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of the present invention will be described below with reference to the accompanying drawings.

FIG. 1 is a block diagram showing an example of a circulating fluidized bed boiler. In the figure, the same parts as those in FIG. 2 are designated by the same reference numerals, and detailed description thereof will be omitted.

In this embodiment, the cyclone 4 is connected to the air line 9 connected to the lower part of the furnace 1 via the air preheater 7 which uses the exhaust gas discharged from the cyclone 4 as a heat source.
A tertiary air line 24 connected to the inlet 4b of the cyclone 4 via a control valve 23 is provided, and the tertiary air (combustion air) C is supplied from the tertiary air line 24 to the inlet 4b of the cyclone 4 to burn unburned components. I am trying to help.

When the tertiary air C is introduced from the tertiary air line 24 to the inlet 4b of the cyclone 4, the swirling flow generated in the cyclone 4 mixes the tertiary air C and unburned matter well, Combustion of unburned components in the cyclone 4 is significantly promoted.

Therefore, according to the above-described embodiment, the unburned portion that has not been completely burnt in the furnace 1 can be actively burned in the cyclone 4 to be greatly reduced, that is, the source of dioxin generation. Since the precursor having a phenolic structure can be thermally decomposed, the generation of dioxins can be significantly reduced as compared with the conventional case.

Further, as shown in this embodiment, if the tertiary air line 24 is attached to the air line 9 passing through the air preheater 7 using the exhaust gas discharged from the cyclone 4 as a heat source, the tertiary air line 24 is discharged from the cyclone 4. The heat of the exhaust gas can be effectively used to preheat the tertiary air C.

The circulating fluidized bed boiler of the present invention is not limited to the above-mentioned embodiment, and various modifications may be made without departing from the scope of the present invention.

[0028]

According to the circulating fluidized bed boiler of the present invention described above, various excellent effects as described below can be obtained.

(I) The unburned components remaining in the furnace, which cannot be completely burned, can be significantly burned in the cyclone to be greatly reduced, that is, the precursor of the phenol structure which is the source of dioxins can be reduced. Because it can be pyrolyzed,
It is possible to significantly reduce the generation of dioxins compared to the conventional one.

(II) If the air line is connected to the inlet of the cyclone via an air preheater using the exhaust gas discharged from the cyclone as a heat source, the heat of the exhaust gas discharged from the cyclone is effectively used. It can be used to preheat the tertiary air.

[Brief description of drawings]

FIG. 1 is a schematic diagram showing an example of an embodiment for implementing the present invention.

FIG. 2 is a schematic view showing an example of a conventional circulating fluidized bed boiler.

FIG. 3 is a diagram showing a structural formula of a precursor having a phenol structure.

FIG. 4 is a diagram showing a structural formula of polychlorinated dibenzoparadioxin (dioxin).

FIG. 5 is a diagram showing a structural formula of polychlorinated dibenzofuran (dioxin).

[Explanation of symbols]

 1 Furnace 3 Bed material 4 Cyclone 4b Inlet 7 Air preheater 24 Tertiary air line (air line) C Tertiary air (combustion air)

Claims (2)

[Claims] 1. The fuel for producing waste is combusted in a furnace while being fluidized together with the bed material, and the exhaust gas generated by the combustion is guided to a cyclone connected to the upper part of the furnace to separate the bed material and then discharged. A circulating fluidized bed boiler configured to circulate the bed material separated by the cyclone to the bottom of the furnace, wherein an air line for introducing combustion air is provided at an inlet of the cyclone. . 2. The air line is connected to the inlet of the cyclone via an air preheater using the exhaust gas discharged from the cyclone as a heat source.
The circulating fluidized bed boiler according to 1.