JPH1182968A - Rdf fired circulation fluidized bed furnace - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a circulation fluidized bed furnace suitable for firing rigidified dirt fuel (RDF). SOLUTION: The RDF fired circulation fluidized bed furnace comprises a swirl combustion chamber 2 comprising a tubular riser section 1 provided with a gas diffuser 7a on the bottom, a tubular section 2a, and a reverse truncated conical hopper section 2b coupled to the lower part thereof wherein a connecting pipe 11 is connected from the top of the riser section 1 to the tubular section 2a in the tangential direction a return pipe 3 is connected to the lower end of the hopper section 2b and a gas discharge pipe 10 is connected to the center of the upper surface, and an outer heat exchanger 4 comprising a gas diffuser 7b provided on the bottom and an inner overheat steam pipe 9 and disposed continuously to the return pipe 3 while being connected with an overflow pipe 12 for returning the overflowing fluid medium back to the riser section wherein the ratio of gas storing time in the riser section 1 to gas storing time in the swirl combustion chamber 2 is set in the range of 1.4-2.2.

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 furnace suitable for burning solid waste fuel (hereinafter referred to as "RDF" (Refuse Derived Fuel)) to recover energy.

[0002]

2. Description of the Related Art In recent years, as a measure against dioxin, a large-scale waste incinerator has been required. With the widespread collection of garbage, it is preferable to convert the garbage collected for each municipality into RDF, bring it to a large-scale refuse incinerator that operates 24 hours a day, incinerate it, and perform power generation and hot water supply.

[0003] RDF is obtained by mixing a small amount of lime with combustible waste such as dry garbage, paper and plastic and compressing it into a lump having a size of, for example, 10 mmφ × 50 mmL. To burn RDF, a stoker type incinerator or a bubbling type fluidized bed furnace is used.

[0004]

SUMMARY OF THE INVENTION A stoker-type incinerator is
Since the heat load on the stalker cannot be increased so much, there are problems such as an increase in the size of the apparatus and the necessity of providing large-scale equipment outside the furnace for desulfurization and denitration. The bubbling type fluidized bed furnace (the operating principle is shown in Fig. 3) is equipped with a heat transfer tube in the I fluidized bed, and has a high heat transfer coefficient, so it requires less heat transfer surface. Small size, no need for flue gas desulfurization equipment by K furnace desulfurization, low thermal NOx generation due to low temperature combustion,
Although the two-stage combustion has advantages such as the reduction of NOx and the removal of dioxin, the combustion of RDF may generate corrosive gas such as hydrogen chloride gas HCl. The heat transfer tube has a problem that its life is extremely short due to a synergistic effect of mechanical abrasion by a fluid medium (such as silica sand) and chemical corrosion by the corrosive gas.

On the other hand, a circulating fluidized-bed furnace (the operating principle is shown in FIG. 4) realizes high combustion efficiency by recirculating I-projected particles, and can increase the hearth load, so that the furnace can be downsized. Coal with a high fuel ratio (fixed carbon / volatiles) with high limestone utilization rate and good desulfurization performance due to complete circulation of projecting particles (fuel ratio is approximately 1.6)
There are various problems when using a circulating fluidized bed furnace designed for incineration of RDF having a low fuel ratio (fuel ratio is approximately 0.15).

That is, RDF having a higher volatile content than coal
In combustion, it takes time to completely burn volatiles in the I riser section, and natural gas such as CO generated in the riser section becomes
When burning lump coal of about 10 mm under in the J riser part, which is easily discharged out of the system through the cyclone, is operated at a gas velocity of 5-6 m / s to circulate the fluid medium,
If the gas residence time is about 4 seconds, the riser is 20-25m
Is required, and the construction cost of buildings and the like increases,
It is not necessary to raise the riser section in such a low fuel ratio fuel as RDF.

The present invention has been devised in view of the above-mentioned problems of the prior art, and performs COD by performing the combustion of RDF volatiles in two stages, a riser section and a swirl combustion chamber. It is an object of the present invention to provide an RDF-fired circulating fluidized-bed furnace capable of preventing unburned gas and dioxin from being discharged outside a room and reducing the height of a riser section.

[0008]

In order to achieve the above object, an RDF-fired circulating fluidized bed furnace of the present invention comprises a tubular and tall riser section having a diffuser plate at the bottom, and a cylindrical section and a lower section connected to the riser section. And a connecting pipe is connected tangentially from the top of the riser section to the side surface of the cylindrical section, and a return pipe is connected to the lower end of the hopper section. And a swirling combustion chamber to which a gas discharge pipe is connected at the center of the upper surface of the cylindrical portion, and which is connected to the lower end of the return pipe, has a diffuser plate at the bottom, and has a superheated steam pipe inside,
An RDF-fired circulating fluidized-flow furnace comprising an external heat exchanger connected to an overflow pipe for returning an overflowed fluid medium to the riser section, wherein a ratio of a gas residence time in the riser section to a gas residence time in the swirl combustion chamber is increased. 1.4 to 2.2
It has become.

Next, the operation of the present invention will be described. Part of the combustion of volatiles generated in the riser during RDF combustion is shared by the swirling combustion chamber. In the swirling combustion chamber, the swirling flow allows good mixing of air and volatiles, so that the volatiles are completely burned, and unburned CO gas and dioxin are not discharged outside the room, and the height of the riser portion is not increased. Can be lowered. In addition, since RDF has a low fixed carbon content, the char as seen in coal burning does not burn in the external heat exchanger. Therefore, in the external heat exchanger, only the fluidized medium forms a fluidized bed, and corrosive gas such as HCl, which may be generated during combustion of RDF, is not generated in the external heat exchanger. There is no problem of corrosion of the superheated steam pipe provided in the vessel. According to experiments,
Preferably, the ratio of the gas residence time in the riser section to the gas residence time in the rotating combustion chamber is between 1.4 and 2.2. In the case of a coal-fired circulating fluidized bed furnace, this ratio is 3.8 to 5.0.

[0010]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS One embodiment of the present invention will be described below with reference to the drawings. FIG. 1 is a cross-sectional view of an RDF-fired circulating fluidized-bed furnace of the present invention, and FIG. 2 is a view taken along the line AA of FIG. In these figures, 1 is a riser section,
It has a tall cylindrical shape. An air diffusion plate 7a is provided at the bottom of the riser portion, and combustion air is sent from the air supply fan 5 to the lower portion of the air diffusion plate 7a via an air pipe 6. An RDF inlet 1 a is provided on a lower side surface of the riser unit 1. A heat transfer tube 8 for steam heating is provided on a wall surface of the riser unit 1. Reference numeral 1b denotes a secondary air supply port provided on a side surface of the riser unit 1, to which an air pipe 6 is connected. One end of a connection pipe 11 is connected to the top of the riser unit 1. A tertiary air supply port 11 a is provided in the connection pipe 11.

Reference numeral 2 denotes a swirling combustion section, and the upper portion is a cylindrical section 2
a, the lower portion is an inverted frustoconical hopper portion 2b.
The other end of the connection pipe 11 is connected to the side surface of the cylindrical portion 2a obliquely downward and in the connection direction. The return pipe 3 is connected to the lower end of the hopper section 2b, and the gas discharge pipe 10 is connected to the upper surface of the cylindrical section 2a.

Reference numeral 4 denotes an external heat exchanger connected to the lower end of the return pipe 3. A diffuser plate 7b is provided at the bottom of the external heat exchanger 4. The lower part of the diffusing plate 7b is
The chambers are partitioned, and an air supply pipe 6 is connected to each chamber so that the pressure in the chamber can be adjusted separately. A bubbling type fluidized bed 4a is formed in the external heat exchanger 4 by air sent through the diffuser plate 7b, and a superheated steam pipe 9 is provided in the fluidized bed 4a. The fluid medium that has overflowed the fluidized bed 4 a is returned to the riser unit 1 via the overflow pipe 13.

Next, the operation of this embodiment will be described. RDF
Is fed into the riser unit 1 from the RDF inlet 1a. In the riser section 1, the combustion gas flows upward from below at a speed of 5 to 6 m / s by the air passing through the diffuser plate 7a, whereby the fluid medium also flows upward from below. . The RDF burns while emitting volatiles in one section of the riser. Volatile substances emitted from the RDF mix with the secondary air supplied from the side surface of the riser unit 1 and burn. The residence time of the combustion gas in the riser section 1 is preferably 2.8 to 3.3 seconds. The combustion gas and the flowing medium flow tangentially into the swirl combustion chamber 2 from the top of the riser section 1 via the connection pipe 11. I do.
The combustion gas mixes with the tertiary air supplied from the middle of the connection pipe 11 and completely burns in the swirl combustion chamber 2. Swirling combustion chamber 2
Inside, the swirling flow favorably mixes air and unburned gas, so that even if the amount of residual oxygen in the exhaust gas at the outlet of the swirling combustion chamber 2 is 5 to 6%, complete combustion occurs, and CO gas, dioxin, etc. Will not be discharged outside the room. The residence time of the combustion gas in the swirling combustion chamber 2 is preferably 1.5 to 2 seconds. Therefore, the ratio of the gas residence time in the riser unit 1 to the gas residence time in the swirl combustion chamber 2 is preferably 1.4 to 2.2.

The hot fluid medium separated in the swirling fuel chamber 2 falls through the return pipe 3 into the external heat exchanger 4. In the external heat exchanger 4, a bubbling type fluidized bed 4a is formed on a diffuser plate 7b, and a superheated steam pipe 9 is installed in the fluidized bed 4a. Only the fluidized bed medium is present in the fluidized bed 4a, and there is no generation of corrosive gas. Therefore, the life of the superheated steam pipe 9 is long. The fluid medium that has overflowed the external heat exchanger 4 is returned to the riser unit 1 through the overflow pipe 13.

The present invention is not limited to the embodiment described above, and various modifications can be made without departing from the gist of the invention.

[0016]

As described above, in the RDF-fired circulating fluidized bed furnace of the present invention, in view of the fact that the fuel ratio of RDF is extremely small as compared with coal, a part of the combustion of volatiles in the riser is swirled. By sharing the chambers, the height of the riser portion is reduced and the emission of unburned CO and dioxin is reduced, so that there is an excellent effect that construction costs of buildings and the like can be reduced and pollution can be reduced.

[Brief description of the drawings]

FIG. 1 is a side sectional view of an RDF-fired circulating fluidized bed furnace of the present invention.

FIG. 2 is a view as viewed in the direction of arrows AA in FIG. 1;

FIG. 3 is an operation principle diagram of a conventional bubbling type fluidized bed furnace.

FIG. 4 is an operation principle diagram of a conventional coal-fired circulating fluidized bed furnace.

[Explanation of symbols]

 REFERENCE SIGNS LIST 1 riser part 2 rotating combustion chamber 3 return pipe 4 external heat exchanger 7 diffuser plate 9 superheated steam pipe 10 gas discharge pipe 11 connection pipe 13 overflow pipe

──────────────────────────────────────────────────の Continued on the front page (51) Int.Cl. ⁶ Identification code FI F23G 5/46 ZAB F23G 5/46 ZABZ (72) Inventor Hirokatsu Nakagawa 2-1-1 Toyosu, Koto-ku, Tokyo Ishikawajima-Harima Heavy Industries Co., Ltd. Inside the Tokyo First Factory

Claims (1)

[Claims] 1. A riser portion having a cylindrical shape and a tall portion having a diffuser plate at a bottom portion, a cylindrical portion and an inverted frustoconical hopper portion connected below the riser portion. A connecting pipe is connected tangentially to the side surface of the cylindrical portion, a return pipe is connected to the lower end of the hopper portion, and a swirling combustion chamber connected to a gas discharge pipe at the center of the upper surface of the cylindrical portion. ,
An external heat exchanger connected to the lower end of the return pipe, having an air diffuser plate at the bottom, having a superheated steam pipe inside, and having an overflow pipe connected to return the overflowed fluid medium to the riser section. An RDF-fired circulating fluidized-bed furnace, wherein the ratio of the gas residence time in the riser section to the gas residence time in the swirling combustion chamber is 1.4 to 2.2.