JPS642154Y2 - - Google Patents

Description

[Detailed Description of the Invention] [Field of Application of the Invention] This invention relates to a carbon reburning furnace suitable for reburning unburned carbon.

[Background of the idea]

Conventional carbon re-combustion furnace (hereinafter referred to as CBC) installed in a 20t/h pilot plant
A schematic cross-sectional view of is shown in FIG. The ash supplied as fuel to the CBC contains 30 to 40% unburned carbon.
%, fine limestone 20-30% and coal ash 35-50%, and the particle size distribution is as shown in Figure 2. These ashes sent to the CBC function to transport the unburned carbon, and also to perform a desulfurization function using Ca contained in the fine limestone and coal ash. The particle size distribution of the ash after combustion is shown in Figure 3. Normally, this ash must be discharged out of the furnace together with the exhaust gas, but in the case of conventional CBC, the furnace has a water-cooled wall structure. In addition, the exhaust gas temperature is cooled by the hollow heat exchanger tube 8 installed at the furnace outlet 10, dropping from about 1000°C to about 250°C, and the exhaust gas flow rate also drops from 1.3 m/s to 0.07 m/s. For this reason, about 40% of the ash particle size distribution shown in Figure 3 falls below the terminal velocity, so they cannot be dispersed and flow backwards to the fluidized bed 4. If this phenomenon continues, the ash particle size distribution in the fluidized bed 4 part The drawback was that the heat balance was disrupted, making it inoperable.

[Purpose of invention]

The purpose of this invention is to eliminate the drawbacks of the prior art described above and to provide a CBC that can be operated without worsening carbon combustion.

[Summary of the idea]

In short, this idea maintains the exhaust gas flow velocity so that the fly ash does not fall below its terminal velocity.

[Example of the invention] This invention will be explained below based on the drawings. FIG. 4 shows a schematic cross-sectional view of an embodiment of this invention, in which an air distribution plate 3 is provided on the wind box part 2 in the CBC main body 1, and a fluidized bed 4 is provided on the air distribution plate 3. is formed. Reference numeral 6 denotes an ash supply nozzle that penetrates the wind box section 2 and projects above the air distribution plate 3 so as to supply supply ash 5 serving as fuel to the fluidized bed 4. The ash supplied into the fluidized bed 4, which has been heated and heated in advance by the ash supply nozzle 6, burns unburned carbon in the ash. In this case, the coal ash and fine limestone that are not combusted have a particle size distribution as shown in Figure 3 above, which is lower than the terminal velocity (particle scattering velocity) caused by the combustion exhaust gas 7 flowing at a constant flow rate from the fluidized bed 4. The fly ash 5a having a particle size of
is discharged to the outside. This is because the flue gas 7 emitted from the fluidized bed 4 requires a certain residence time, so while it passes through the cavity section 8, heat is absorbed by the surrounding water wall pipes (not shown). that it might be done. This temperature drop of the combustion exhaust gas 7 is
The flow velocity of the exhaust gas is also slowed down, which in turn reduces the particle size of the scattered ash particles, and the ash below the scattering flow velocity cannot be scattered and falls again. For this purpose, it is necessary to make the cross-sectional area of the empty tower section 8 smaller than the cross-sectional area of the fluidized bed 4 portion, and to set the flow velocity of the combustion exhaust gas 7 at the highest part of the empty tower section 8 to be less than the ash scattering speed. be. In addition, the empty tower heat exchanger tube 9 is connected to the combustion exhaust gas 7.
The ash is placed on the downflow side of the fluidized bed 4 to prevent the ash from falling into the fluidized bed 4 again even if the exhaust gas temperature decreases and the exhaust gas flow rate becomes lower than the ash scattering speed.

With this configuration, unburned carbon can be burned efficiently, and the main furnace (not shown)
In addition to improving the overall combustion efficiency in conjunction with be able to.

FIG. 5 shows another embodiment. In this case, a water-cooled wall (not shown) in the tower section 8 is installed so that the flow rate of the exhaust gas at the furnace outlet 10 can be kept higher than the ash scattering speed.
In order to prevent the flow rate of the exhaust gas from decreasing due to the temperature of the exhaust gas due to the heat exchanger tubes 9 or lower, the cross-sectional area of the cavity section 8 is made small.

[Effect of idea]

As explained above, according to this invention, the effect that unburned carbon can be efficiently combusted can be obtained.

[Brief explanation of the drawing]

Figure 1 is a schematic cross-sectional view of a conventional CBC, Figure 2 is a relationship between the particle size distribution of ash supplied to the CBC and the particle size scattering speed, and Figure 3 is a diagram showing the relationship between the particle size distribution of ash supplied to the CBC and the particle size scattering speed. Figure 4 is a schematic cross-sectional view of one embodiment of this invention, and Figure 5 is a schematic cross-sectional diagram of another embodiment of this invention. shows. Explanation of symbols, 1... CBC body, 2... Wind box section, 3
... Air distribution plate, 4... Fluidized bed, 5... Ash, 6... Ash feeding nozzle, 7... Combustion exhaust gas, 8... Vacant column section, 9... Vacant column section heat exchanger tube, 10... Furnace outlet.

Claims (1)

[Scope of utility model registration request] In a carbon reburning furnace that fluidizes unburned carbon in the ash discharged from a fluidized bed combustion furnace,
A carbon reburning furnace characterized in that an ash feeding nozzle is provided in the lower part of the furnace, and the cross-sectional area of the upper empty tower part is smaller than the cross-sectional area of the lower fluidized bed part.