JPS5811522B2 - Fluidized bed combustion equipment - Google Patents

Description

[Detailed description of the invention] The present invention relates to a fluidized bed combustion apparatus.

As shown in FIGS. 1 to 6, a conventional fluidized bed combustion apparatus has a wind box 8 consisting of a furnace bottom 7 and side walls 6, a furnace wall 9, and a ceiling 10.
It consists of furnaces 1 and 2 consisting of.

Of these, region 1 in the furnace is a region where fluidized material particles exist, which is a fluidized bed, and region 2 is a gas phase region, which is called a freeboard.

An air distribution plate 3 is provided between the wind box 8 and the furnace 1.

Representative examples of air distribution plates are shown in FIGS. 3 to 5.

The one shown in Figure 3 is a flat plate with holes (generally circular holes) drilled at equal intervals, the one shown in Figure 4 has slits, and the one shown in Figure 5 has holes above the holes. It is equipped with a cap.

A plurality of long and short tubes 5 are attached to the furnace wall 9 so that their tips reach near the air distribution plate (50 to 100 mm) at equal intervals, and are called fluid particle supply tubes.

Fuel and fluid particles are supplied together with air 12 through this fluid particle supply pipe 5 .

The specific structure of the air distribution plate 3 is of the scattered type as illustrated in Figures 3 to 5, but when viewed from the perspective of the entire furnace, it can be seen as a flat plate with ventilation holes evenly provided. I can do it.

13 is a fluid discharge pipe when lowering the fluidized bed 1, and 14 is a metering valve.

As shown in FIG. 7, which shows the combustion situation in the fluidized bed 1, fuel particles, particles of fluidized material such as limestone are transported through the supply pipe 5 by air in an amount of about 1/20 of the total amount of air supplied to the furnace. It is blown into the lower part of the fluidized bed (above the air distribution plate) and is evenly distributed along the air distribution plate 3 as shown by arrow 24.

Air 20 is uniformly supplied from below through the air distribution plate 3.

The injected fuel is heated to a high temperature (800-100 m
By c), the volatile matter in the fuel begins to vaporize.

21 conceptually shows the positions of volatile components.

The volatilized gas obtains air supplied from below and blows directly upward while burning (arrow 22).

The solid content (mainly carbon, hereinafter referred to as char) in the fuel burns up while repeatedly circulating up and down as shown by arrow 23 within the fluidized bed 1 region.

Figure 8 shows the oxygen concentration distribution in the furnace height direction.

The volatile matter has a high ability to generate nitrogen oxides, and the volatile matter has a high ability to generate nitrogen oxides.
Volatile gas that begins to be generated in the vicinity mixes with air and burns in a wide oxygen concentration atmosphere A along curve 30 in Figure 9.
Especially in the high oxygen concentration region (conceptually indicated by A), a large amount of NO
Generate x.

On the other hand, char also burns in the same atmosphere.As shown by curve 31 in FIG. 9, char's ability to generate nitrogen oxides is small and its contribution to the total NOx is small.

However, there was a drawback that a large amount of NOx was generated in an integrated manner.

Therefore, the present invention was made with the object of developing a fluidized bed combustion apparatus that reduces nitrogen oxides in waste gas discharged from a fluidized bed combustion furnace.

That is, in the present invention, the flow material particle supply pipe is placed on an air distribution plate having a downward opening, surrounding the opening of the supply pipe,
A cylindrical bamboo dike with only a small opening at the bottom is provided, and a char supply pipe is installed between adjacent diversion dikes to supply only fine powder char, so that the fluidized material particles to be burned are diverted. There will be a partial oxygen shortage above the embankment,
The object of the present invention is to provide a fluidized bed combustion apparatus in which the entire fluidized bed combustion furnace generates low NOx.

Next, the present invention will be explained based on an embodiment shown in FIGS. 10 to 18.

Cylindrical combustion jet deflection banks 50 are arranged at equal intervals on the air distribution plate 3 so as to surround the tip of the fluid particle supply pipe 5, the bottom of the deflection bank 50 is closed, and only a portion of the deflection bank 50 is cut up at the bottom.
2 is provided.

The raised portion 52 is located on the insertion side of the fluid particle supply pipe 5, and the height of the deflection bank 50 is lower than the height of the fluidized bed 1.

A new particulate char supply pipe 51 is provided so as to open into the intermediate portion of the adjacent deflection banks 50.

Next, the operation of this device will be explained based on FIGS. 14 to 17.

The jet stream 24 containing the fuel blown out together with the air 12 from the fluid particle supply pipe 5 is deflected upward by the action of the deflector bank 50 .

The gas evaporated under the high temperature of the fluidized bed 1 of deflected fluidized material particles flows up the freeboard 2 as an upward flow indicated by an arrow 22.
The best one comes out.

The area between which this volatile gas is discharged is the area surrounded by dotted lines 63.

The char component from which the volatile matter has been removed repeats vertical circulation as shown by the arrow 23, is uniformly distributed within the fluidized bed 1, and is burned out.

The volatile gas 22 discharged to the freeboard 2 is combusted by oxygen diffusing from outside the dotted line 63.

On the other hand, from the particulate char supply pipe 51, char smaller than the fluidized material particles is blown in, heated and burned in the fluidized bed 1 as shown by arrow 60, and discharged to freeboard 2 as shown by arrow 61.

The cutout portion 52 functions to discharge the fluidized material particles accumulated in the diversion bank 50 when the height of the fluidized bed 1 is lowered.

Under normal operating conditions, the amount of air introduced throughout the fluidized bed is 10 to 20 times greater than the stoichiometric amount required for combustion of the fuel.

The fuel is supplied from the fluid particle supply pipe 5, but the jet stream 24
Since the dispersion of the air is limited within the deflection bank 50 at the outlet of the supply pipe 5, an air shortage occurs in this portion.

On the other hand, only char exists outside the embankment 50, creating a state of excess air.

Curve A in FIG. 15 represents the 02 concentration distribution corresponding to the height direction of the furnace on the line AA in FIG. 14, and curve B represents the distribution on the same <B-B line.

A dotted line 26 indicates the upper surface of the combustion furnace 1.

A portion of the volatile matter generates NOx at the bottom of the fluidized bed 1 as shown in range A of curve 30 in FIG.
Free board 2 in Figure 4 is used to perform diffusion combustion.

In the freeboard 2, in the area sandwiched between the dashed line 62 and the dotted line 63, fuel (volatile gas, indicated by F in FIG. 14) and oxygen (02) coexist and burn, as shown in the upper graph of FIG. , the oxygen concentration in this region is low, and range B in Figure 9
The amount of NOx generated is limited to that shown in .

On the other hand, char combustion is performed in an atmosphere with a higher oxygen concentration than in the conventional method (Fig. 9, range C of curve 31).
However, since the ability to generate NOx is small, NOx does not increase significantly.

The gist of the above is shown again in FIGS. 16 and 17.

Figure 16 shows the appearance of NOx generation in volatile matter.
The volatile matter combustion rate is indicated by (η■).

FIG. 17 shows the NOx generation state of char, and shows the combustion rate of char as (η■).

In FIG. 16, 70 is the NO of volatile matter according to the prior art.
Most of the 1 in the x distribution occur within the fluidized bed 1.

71 is the NOx distribution of volatile matter according to the present invention, and in the volatile region in the fluidized bed 1 (inside and above the deflection bank 50), oxygen disappears at a certain height, and the generation of NOx temporarily becomes zero (indicated by point 73). .

The volatile matter that escaped into Freehold 2 undergoes diffusion combustion and becomes 72N.
Generates Ox.

In FIG. 16, the area occupied by diagonal lines 71 and 72 (the total amount of NOx generated by the technology of the present invention) is much smaller than the area below 70 (the total amount of NOx generated by the conventional technology).

On the other hand, in the area within the fluidized bed 1 where the char is burned (the area outside the bank 50), the oxygen concentration is higher than in the conventional method.
As shown in the figure, NOx75 is higher than the conventional NOx74.

However, since the NOx generation ability of the volatile components is much greater than that of char, the total amount of NOx produced by the present invention is less than that of the conventional method.

Next, a fluidized bed combustion plant to which the fluidized bed combustion apparatus according to the present invention is practically applied will be described with reference to No. 18.

This plant includes a fluidized bed combustion device 80, a char combustion furnace 81,
Consists of a solid-gas separator 83, waste gas discharge passages 91°92,
The structure of each device is as follows.0 The fluidized bed combustion device 80 is supplied with fluidized material particles through the supply pipe 5.

At the opening of the supply pipe 5. A deflection bank 50 is provided, and a fine powder char supply pipe 51 is connected to the outside of the deflection bank 50.
are arranged and are configured similarly to the first embodiment.

The char combustion furnace 81 is a combustion furnace exclusively for char, and the supply pipe 90
char is supplied and combusted with air.

The solid-gas separator 83 introduces the exhaust gas from the fluidized bed combustion apparatus 80 through the flue 82, sieves off only the solid fine powder char, and distributes it to the pipe 90 and the pipe 85.

The fine powder char distributed to the pipe 85 is mixed with the fine powder char stored in the hopper 86, one of which is supplied to the fine powder char supply pipe 51, and the other is supplied from the pipe 89 via the pipe 88. The mixed fluid particles are mixed with the fluidized material particles and supplied to the supply pipe 5.

The waste gas discharge path 91 is connected to the solid-gas separator (cyclone) 83.
Emit more waste gas.

The waste gas discharge passage 92 discharges combustion waste gas from the char combustion furnace 81 .

It is well known that coke is a strong reducing agent for NOx in a high temperature range close to 1000°C (Journal of Japan Fuel Association Vol. 54, No. 581, p. 766).

Therefore, the fine particles obtained by crushing coke are stored in the hopper 86, and the fine particles are supplied to the fluidized bed combustion furnace 80 through the fine powder char supply pipe 51.
At the same time, the fine powder char obtained by the cyclone 83 is also supplied via the conduit 85.

Further, if necessary, the particles are mixed with the fluidized material particles supplied through the pipe line 89 and combusted.

In the char combustion furnace 81, only char is burned, so N
There is no need to consider the generation of OxG).

In this way, a fluidized bed combustion system that suppresses the generation of NOx is constructed and put into practical use.

[Brief explanation of drawings]

Figure 1 is a front sectional view of a conventional fluidized bed combustion apparatus, Figure 2 is a view taken along the ■-■ arrow in Figure 1, and Figures 3 to 5 are enlarged views of the ■ section in Figure 1, respectively. , Fig. 6 is an enlarged view of the ■ part in Fig. 2, Fig. 7 is a diagram showing the combustion state of the conventional device, and Figs. 8 and 9 show the furnace position, 02 concentration, A02 concentration, and NOx concentration, respectively.
FIG. 10 is a front sectional view of one embodiment based on the present invention, and FIG. 11 is a diagram showing the amount of generation.
The arrow view, Figure 12 is the ■-■ arrow view in Figure 10, Figure 13
The figure is an enlarged view of part ■ in Figure 11, Figure 14 is a diagram showing the combustion state of the example, Figures 15 to 17 are graphs showing the effects of the example, and Figure 18 is an example of the example in an actual plant. The block diagram when placed in is shown. 1...Fluidized bed, 2...Free board,
3... Air distribution plate, 5... Fluidized material particle supply pipe, 7... Furnace bottom, 8... Wind box, 9
... Furnace wall, 10 ... Ceiling, 13 ...
... Fluid material discharge pipe, 14... Metering valve, 50.
...Deflection bank, 51...Fine powder char supply pipe.

Claims (1)

[Claims] 1. In a fluidized bed combustion furnace consisting of an air distribution plate equipped with numerous holes that supplies air from below, and a plurality of fluidized material particle supply pipes that are opened downward on the air distribution plate and supply fluidized material particles. , a cylindrical deflection bank with an open upper part and a closed lower part is provided surrounding the opening of the fluid particle supply pipe, and openings of a plurality of fine powder char supply pipes are arranged outside the deflection bank. A fluidized bed combustion device characterized by: