JPS599004B2 - Fluidized bed combustion control method - Google Patents

Description

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

Fluidized bed combustion allows for the following: 1. In-furnace desulfurization using dolomite or lime is possible at the same time as combustion.

2. Low-temperature combustion produces less NOx.

3. The heat transfer coefficient of the heat transfer surface immersed in the fluidized bed is large.

Because of these advantages, it is said to be particularly suitable for burning heavy oil, coal, etc., and is viewed as promising.

Now, when burning coal with a high sulfur content, the SOx in the exhaust gas can be reduced to almost zero by desulfurization at the same time as the combustion, but coal with a high sulfur content usually also has a high nitrogen content, so When this is burned, NOx reaches 150 to 200 ppm since simultaneous denitrification is not possible. Currently, there is a technology to reduce NOx in flue gas using flue gas denitrification equipment, and in particular, dry catalysts are used to reduce NOx in flue gas.
It is considered advantageous to reduce x to N2, but this equipment requires high equipment and operating costs and is complicated to handle.

Because of this, it is possible to remove NOx at the same time as combustion, or NO
There is a need for fluidized bed combustion that can extremely reduce the amount of x produced.

On the other hand, two-stage combustion is effective in combusting a fuel containing a large amount of nitrogen such as coal so as to reduce the amount of NOx produced, but when two-stage combustion is applied to fluidized bed combustion, NOx
Although the amount of x produced decreases, in-furnace desulfurization, which is an advantage of fluidized bed combustion, deteriorates.

This is because in-furnace desulfurization achieves the chemical reaction of 502 + [CaCO3 + MgO] force p2 → [caso2 + MgO] + CO2, but in two-stage combustion, oxygen is reduced in the first stage of combustion, so the above equation This is because no reaction occurs, and even if the amount of oxygen is increased in the second stage combustion, the reaction time is insufficient.

Therefore, it is necessary to perform fluidized bed combustion so that denitrification can be performed simultaneously with combustion, or to reduce the generation of NOx, without degrading the desulfurization that is performed simultaneously with the combustion.
Therefore, as a result of intensive research to develop a technical means that can satisfy this requirement, the inventor of the present invention created a multi-stage fluidized bed, and achieved NOx generation through partial combustion of fuel in the first stage fluidized bed. The subsequent multi-stage combustion of combustible gas in the fluidized bed almost eliminates the production of NOx and reduces HCN.
The present invention has discovered a combustion control method for a fluidized bed that can almost completely decompose harmful gases such as combustible gases and desulfurize SO2 and H2S by completely burning the combustible gas in the final stage fluidized bed.

The air ratio in combustion of fuel in the first stage fluidized bed will be explained with reference to FIG.

Figure 1 shows the gas composition in an equilibrium state versus air ratio when residual oil with S3.5% is gasified.
According to this, it can be seen that in order to reduce NOx, it is sufficient to lower the air ratio. In other words, it turns out that two-stage combustion is sufficient. However, if this is done, desulfurization deteriorates as described above. Further, when the air ratio λ<0.5, NOx generation is completely eliminated and SO2 is almost eliminated, but a large amount of H2S and COS are generated. Furthermore, when the air ratio λ is set to 0.5 to 0.7, almost no NOx is generated, but SO2, H2S, CO
A large amount of S is emitted. Furthermore, air ratio λ=0.7~0
．． When it is set to 75, almost no NOx is generated, and although a large amount of SO2 is generated, H2S and COS are hardly generated. Therefore, in the present invention, the fuel is partially combusted at an air ratio λ of 0.4 to 0.7 in the first stage fluidized bed.
Only a small amount of NOx is produced, and a large amount of SO2 and H2S are produced. Also, the air ratio and temperature of the second stage fluidized bed will be explained.

Although the present inventor is not a fluidized bed, it is a multi-stage furnace, in which spaces composed of fireproof walls are connected via lattice-like fireproof walls, and the combustible gas partially combusted in the upstream is newly supplied with air in each space and is partially combusted. It was found that by adjusting the amount of air supplied to each stage and adjusting the amount of combustion, the final NOx value was found to be extremely low.・In the N invention, this phenomenon is applied to a multistage fluidized bed to optimize the air amount and temperature in each stage. For example, when coal is used as fuel, the air ratio and temperature in each stage are λ=1.10, layer temperature t2 700-800°C. The fluidized bed combustion control method according to the present invention divides the fluidized bed into two or more stages, and in the first stage fluidized bed, the fuel is transferred to an air ratio λ = 0.4 to 0, where only a small amount of NOx is produced and SO2 and H2S are produced.
．． Partial combustion is performed at step 7.

This partial combustion produces combustible gas, SO2, H2S, and HC.
N, etc. are produced, but when HCN etc. are normally burned, NO is produced.
x, so in the combustion of the first stage fluidized bed in the second and subsequent stages, or the combustion of the second and subsequent stages, the air ratio λ = 1.10 and the temperature t2 700 at which only a small amount of NOx is generated
Most of it decomposes by burning at ~800C. The fluidized medium of the fluidized bed that takes part in this combustion does not need to have a desulfurization effect. However, the combustible gas generated in these fluidized beds is completely combusted in the final stage fluidized bed by increasing the air ratio.
H2S is considerably oxidized and becomes SO2 before it enters the fluidized bed in the final stage, but even if it remains in the form of H2S, it is completely converted to SO2 in the fluidized bed in the final stage, and the SO2 is dissolved into dolomite, etc. in the fluidized medium. It is desulfurized using a desulfurizing material. An embodiment of the present invention will be described below with reference to FIG. 2 in the case of a two-stage fluidized bed.

The fluidized medium in the first stage fluidized bed 1 does not necessarily have to contain a desulfurizing agent, but it is placed on the dispersion plate 2 from below as indicated by the arrow 3.
It is fluidized by the air that is supplied upward as shown in FIG. 4 and the air that is supplied into the fluidized bed 1 as shown by arrow 4.
Fuel such as coal is supplied into the fluidized bed 1 as shown by arrow 5, but the amount of air supplied from below as shown by arrow 3 is smaller than the theoretical air amount for complete combustion of the fuel, for example, about 60%. Substantially, the air ratio λ is approximately 0.5. Therefore, in the first stage combustion part of the first stage fluidized bed 1, very little NOx is produced, and incomplete combustion gas (C
mixed gas such as O2 and CO, H2) and SO2 and H2S
and HCN etc. are generated. These gases are subjected to second-stage combustion by air supplied into the fluidized bed 1 as shown by arrow 4, but by adjusting the amount of air supplied, the air ratio λ = 1,10 By setting the layer temperature to t = 700 to 80°C, even if gases such as HCN that generate 0x are included in normal combustion,
The amount of NOx produced is extremely small, and most of HCN and the like are decomposed. At this time, H2S is also considerably oxidized and SO
It becomes 2. In the space 6 provided above the fluidized bed 1 of the first stage, combustible gas still appears, which is fed to the fluidized bed 7 of the second stage. The fluidized medium in the fluidized bed 7 is fluidized on the distribution plate 8 by the combustible gas supplied from below and the air supplied into the fluidized bed 7 as shown by arrow 9. The fluidized medium of the fluidized bed 7 is composed of a desulfurizing material such as dolomite and sand, and the combustible gas supplied from the upper space of the first stage fluidized bed 1 is combusted by the supplied air as shown by the arrow 9, and at the same time the combustible gas is SO2 in the gas is desulfurized and becomes CasO4. Furthermore, H2S in the combustible gas is removed from the fluidized bed 7 in the second stage.
It is oxidized inside and becomes SO2, which is also desulfurized and becomes C.
It becomes asO4. In the combustion of the combustible gas in the second stage fluidized bed 7, harmful gases such as HCN are completely decomposed, and the amount of NOx produced at this time is extremely small. The gas completely combusted in the second stage fluidized bed 7 flows into the cyclone 11 through the upper space 10, where it is removed from dust and discharged to a chimney (not shown). The dust accumulated in the lower part 12 of the Cytalon 11 passes through a discharge device (not shown) and is transferred to the second stage fluidized bed 7.
or discharged from the system. In the first stage fluidized bed 1, the fluidized medium is consumed or becomes fine, so the arrow 13
The fine particles and ash are discharged as shown by arrow 14. In the second stage fluidized bed 7, the desulfurization material and the fluidized medium are consumed and refined, so they are supplied as shown by the arrow 15, and the CacO
4 is discharged as shown by arrow 16, and ash is discharged as shown by arrow 17. Incidentally, it is possible to provide heat transfer surfaces on the peripheral wall 18 of the first and second stage fluidized beds, within the fluidized beds 1 and 7, within the spaces 6 and 10, etc., to perform cooling and absorb the combustion heat of the fluidized bed. can.

The above example is a two-stage fluidized bed in which two-stage combustion is performed in the first stage fluidized bed 1.
It is possible to carry out multistage combustion of two or more stages (including the space 6 of the soil part), to make the first stage fluidized bed 1 multistage, and also to make the second stage fluidized bed 7 (including the upper space 10). It is also possible to perform multistage combustion.

In short, in the fluidized bed before the final stage fluidized bed, gases such as HCN that may generate NOx in normal combustion are subjected to multi-stage combustion to generate very little NOx.
Furthermore, it is only necessary to adjust the air ratio and combustion temperature to almost completely decompose harmful gases such as HCN and completely burn unburned components, and in the final stage fluidized bed, sufficient air is provided at the same time as combustion. All that is required is to change H2S to SO2 by giving a certain ratio, desulfurize SO2, and completely decompose harmful gases such as HCN. As described in detail above, according to the fluidized bed combustion control method according to the present invention, the generation of NOx can be reduced by partially burning fuel in the first stage of the fluidized bed divided into multiple stages. By performing multistage combustion of combustible gas in the subsequent fluidized bed, it is possible to almost eliminate the generation of NOx, almost completely decompose HCN, etc., and convert H2S in the combustible gas to SO2,
By completely burning the combustible gas in the fluidized bed at the final stage, harmful gases such as HCN remaining in the combustible gas can be completely decomposed, and the remaining H2S and SO2 can be completely desulfurized using the desulfurization material. This eliminates the need for conventional dry catalyst denitrification equipment, which has high equipment and operating costs and is complicated to handle, making it possible to simplify the plant and make effective use of a fluidized bed, which is effective for desulfurization. ,,its practical effects are enormous.

[Brief explanation of drawings]

Figure 1 is a graph showing the gas composition in an equilibrium state versus air ratio when residual oil with S3.5% is gasified, and Figure 2 is a graph for explaining the fluidized bed combustion control method according to the present invention. FIG. 2 is a cross-sectional view of a fluidized bed. DESCRIPTION OF SYMBOLS 1...First stage fluidized bed, 2...Dispersion plate, 6...Space, 7...Second stage fluidized bed, 8... ... Dispersion plate, 10 ... Space, 11
... Cyclone, 12 ... Lower part of cyclone, 18 ... Peripheral wall of fluidized bed.

Claims (1)

[Claims] 1 The fluidized bed is divided into multiple stages, and the fuel is converted to NO in the first stage fluidized bed.
Partial combustion occurs at an air ratio λ = 0.4 to 0.7, where only a small amount of x is produced and SO_2 and H_2S are produced, and the combustible gas produced by this partial combustion is transferred to the fluidized bed after the first stage fluidized bed to produce only a small amount of NOx. Air ratio λ = 1.10 and temperature t = 70 that only generates
Fluidized bed combustion control characterized by multi-stage combustion at 0 to 800°C, complete combustion of combustible gas supplied from the previous fluidized bed in the final stage fluidized bed, and at the same time removing H_2S and SO_2 with a desulfurization material. Method.