JPS589761B2 - How to use the service - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a thermal decomposition treatment of calcium nitrate components that require disposal and calcium nitrate salts produced by-product in wet denitration treatment, and a method for producing NOx by thermal decomposition of nitrates.

Exhaust gas from boilers, combustion furnaces, calciners, etc. contains several hundred ppm of NOx gas, and these NOx gases are extremely harmful and must be removed.

There are two methods for removing NOx gas from exhaust gas: the method of absorbing it with an alkaline absorption liquid (equimolar method), or the method of adding ozone to the exhaust gas and absorbing it with an alkaline absorption liquid or sulfite absorption liquid (ozone method). In this case, nitrates and nitrites are produced as by-products, and these nitrates and nitrites must be treated to render them harmless.

The inventors have already invented a method for thermally decomposing nitrates.

(Patent Application No. 50-106797 (Japanese Patent Application No. 52-3029)
Publication No. 8)).

The key point is to mix calcium nitrate and quicklime, which is a thermal decomposition product of calcium nitrate, in an appropriate ratio and maintain the thermal decomposition temperature between 800° and 1200°C to continuously produce quicklime with good activity. This is where a high concentration of NOx gas is generated.

However, in the above method, continuous thermal decomposition using a rotary continuous heating furnace (hereinafter simply referred to as rotary furnace) is possible, but if the operation continues for a long time, so-called rings are formed, making stable operation difficult. When the ring is heat-treated for a long time, the generated quicklime loses its activity and becomes dead lime.

In general, there are many examples of troubles caused by the formation of rings in the operation of rotary furnaces.

For example, chains are often used to treat baking soda, etc., and thermal decomposition of nitrates is also effective, but the chains also fuse and grow, making it difficult to operate stably for long periods of time. Have difficulty.

Furthermore, as shown in FIG. 1, if a scraping rod with a small clearance is installed in the upper part of the rotary furnace, stable operation for a considerably long period of time becomes possible.

However, in a rotary furnace where the temperature reaches about 1000° C., the scraping rod becomes deflected in a short period of time.

To prevent this, by passing water through a scraping rod, the deflection is prevented and the material fused to the inner wall of the rotary furnace is scraped off, preventing ring growth.

However, due to the heat carried away by the water passing through the scraping rod,
The thermal efficiency of rotary furnaces is significantly reduced and more fuel is required for combustion.

As the size of the rotary furnace increases, the heat dissipated from the shell decreases to about 10% of the total required heat, but as the equipment becomes smaller, the proportion of heat dissipated from the shell increases and reaches 40 to 50% or more.

Therefore, cooling the inside of the scraping rod with water is fatal from the point of view of thermal efficiency, and the NOx concentration in the exhaust gas at the outlet decreases, which increases the scale of the next NOx detoxification process, which is not efficient.

Therefore, a constant amount of air is supplied inside the scraping rod in parallel with the combustion burner to keep the surface temperature of the scraping rod below 700℃.This is because if the scraping rod is left at a temperature exceeding 700℃ for a long period of time, creep will occur. This is because the scraping rod is deformed.

The air discharged in this way is directly introduced into the combustion chamber and used as secondary air for combustion gas, increasing the thermal efficiency of the rotary furnace, thereby increasing the concentration of NOx gas decomposed in the rotary furnace, and also using preheated air. When used as the secondary air of a combustion burner, it forms a long diffusion flame suitable for a rotary furnace combustion burner, and by completely burning in the rotary furnace, the combustion temperature range (
The maximum temperature inside the rotary furnace is slightly closer to the center of the rotary furnace, resulting in a combustion type desirable for thermal decomposition.

According to the present invention, a particularly remarkable effect is exhibited when a mixture of calcium nitrate and quicklime is thermally decomposed in a rotary furnace.

In other words, highly active and homogeneous quicklime is produced continuously,
Moreover, it is possible to generate nitrogen oxides at a high concentration.

Next, the present invention will be explained in detail by way of examples.

Example A powder mixture of calcium nitrate and quicklime = 1:4 (weight ratio) was continuously fed to a rotary furnace to form a decomposition and firing zone of 900 to 900.
Thermal decomposition operation was performed at 50° C. in a direct heating rotary kiln.

Rotary furnace operating conditions L/D=12L=1200, rotation speed 3R, P, M Rotary furnace inclination 3/100, residence time 20 minutes Feedstock7.
5kg/Hr, fuel, propane gas discharge Activity of quicklime 85% (Coarse particle titration method gypsum lime handbook, Gihodo edition P48
4) Decomposition degree: 95% (based on total nitrogen analysis value by Kieldahl method) The operation results are summarized in the following table.

[Brief explanation of the drawing]

Figure 1 is a schematic side view of a rotary furnace with a scraping rod attached to it, Figure 2 is a schematic illustration of a rotary furnace equipped with angle iron and chains, and Figure 3A is a rotary furnace with a scraping rod made of angle iron attached. A schematic side view, and B shows a sectional view. 1... Burner, 2... Scraping stick,
3...Rotary furnace, 4...Ring zone of rotary furnace, 5...Angle iron, 6...Chain, 7
・・・・・・Scraping rod made of angle iron, 8・・・・・・
Pyrolysis sample, A...Air introduction, F1...
・Entrance hood, F2...Exit hood, C...
...CaO.

Claims (1)

[Claims] 1 In a method of decomposing calcium nitrate or a mixture containing calcium nitrate in a rotary continuous heating furnace, a rod-shaped oyster device is attached to the upper part of the rotary heating furnace to prevent the mixture containing calcium nitrate from fusing and ring formation. ,
A fixed amount of air is supplied into the oyster rod to keep the surface temperature of the oyster rod below 700°C to prevent deformation of the oyster rod due to heat, and the heated air discharged from the oyster rod is used for combustion in a rotary continuous heating furnace. It is used as secondary air to form a long diffusion flame of a heating burner suitable for pyrolysis in a rotary continuous heating furnace to smooth the pyrolysis reaction and continuously produce homogeneous quicklime with high activity. , and a method for thermally decomposing nitrates, which is characterized by producing nitrogen oxides at a high concentration.