JPS631889B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an exhaust gas desulfurization method for removing sulfur oxides from combustion exhaust gas from boilers and the like and from sintering furnace exhaust gas from steel plants and the like.

There are two methods for removing sulfur oxides (hereinafter referred to as SOx) from exhaust gas: wet methods and dry methods.
The mainstream wet method is the limestone-gypsum method, but the wet method has problems such as securing water, treating waste liquid, treating by-product gypsum, and increasing the temperature of the process gas, so the dry method has recently been reconsidered.

In this dry method, exhaust gas is desulfurized using a carbonaceous adsorbent such as activated carbon, which is a desulfurizing agent, and is then purified by removing dust using a dust collector.

When desulfurization is performed using a carbonaceous adsorbent, the desulfurization ability gradually decreases due to repeated heating and regeneration of the adsorbent.

Therefore, it is desirable to maintain the desired desulfurization ability of the adsorbent for as long as possible.

Since an inexpensive carbonaceous adsorbent is used in the dry desulfurization method, the initial adsorption capacity of the adsorbent is poor and it is necessary to activate it until the desired adsorption capacity is obtained. Since this takes a considerable amount of time, it is desirable to activate the adsorbent as early as possible before the start of operation of the apparatus.

For this reason, conventionally, in the case of a moving bed system, a method has been adopted in which the amount of adsorbent transferred is increased, but this method has the drawback of increasing consumption of the adsorbent. On the other hand, a method has been proposed in which NH ₃ gas is injected into the exhaust gas in advance and then passed through a carbonaceous adsorbent layer for desulfurization. According to this method, in addition to the advantage that denitrification can be performed by the catalytic action of the carbonaceous adsorbent, the desulfurization ability can be maintained for a long time, chemical consumption during heating regeneration of the adsorbent is reduced, and adsorption,
There is an advantage that activity is improved by repeated reuse.

However, in this method, the gasification of carbon in the carbonaceous adsorbent is relaxed due to the NH ₃ gas injected in advance, and the development of pores etc. is suppressed, resulting in high activation and the desired desulfurization ability. to
It had to take between 1,000 and 2,000 hours.

The inventors of the present invention have made extensive studies in order to provide an exhaust gas desulfurization method that maintains the desired desulfurization ability for a long time and quickly activates the adsorbent to a high degree. As a result, when the desulfurization equipment first started operating, the flue gas was guided to the desulfurization equipment and brought into contact with a carbonaceous adsorbent to remove and inactivate the sulfur oxides in the flue gas without adding ammonia gas to the flue gas. The method is characterized in that after the carbonaceous adsorbent is heated and regenerated and activated by repeated use, ammonia gas is added to the exhaust gas and adsorption and regeneration are repeated.

In carrying out the present invention, either a moving layer type or a fixed layer type of device can be used, but the present invention will be explained below with reference to FIG. 1 using a moving layer type as an example.

In the initial stage of operation of the desulfurization equipment, the exhaust gas to which NH ₃ gas has not been injected is passed through the orthogonal moving bed desulfurization reactor 2 having a carbonaceous adsorption layer such as activated carbon, where it is desulfurized, and then released into the atmosphere through the dust collector 3. released.

In the present invention, since NH ₃ gas is not injected into the exhaust gas at the initial stage of operation, SOx is replaced by O ₂ and H ₂ O in the exhaust gas.
Due to the presence of sulfuric acid, it is adsorbed on the adsorbent as sulfuric acid.
The adsorbent that adsorbed SOx and became inactive is transferred to reactor 2.
When the sulfuric acid is extracted from the bottom of the carbonaceous adsorbent and supplied to the moving bed type adsorbent regenerator 4, and heated with high-temperature inert gas at 300 to 600°C, sulfuric acid is desorbed as SO ₂ according to the following equation, and at the same time, some of the carbon in the carbonaceous adsorbent is becomes gas.

1/2C + H ₂ SO ₄ →SO ₂ +1/2CO ₂ +H ₂ O Along with this, the pores of the carbonaceous adsorbent develop and the specific surface area increases, and it is activated and reused for adsorption. .

After repeating such adsorption and regeneration to some extent, NH ₃ is released into the exhaust gas from the ammonia gas storage tank 1.
Gas is injected to adsorb SOx and regenerate the adsorbent in the same manner as above.

This quickly activates the adsorbent and
And this high activity is maintained for a long period of time.

However, in the present invention, the timing of injecting NH ₃ gas varies depending on the exhaust gas and operating conditions, but is preferably about 100 to 1000 hours after the start of operation of the desulfurization equipment. Especially when the SO ₂ concentration in the exhaust gas is low (approximately
300ppm or less), the amount of adsorbed sulfur is small, and activation takes a long time. Under these conditions, it is recommended to add SO ₂ to the exhaust gas at the beginning of operation and activate it by operating without NH ₃ injection. It is possible to accelerate it.
As a method of adding SO ₂ to the exhaust gas, a part of the highly concentrated SO ₂ gas obtained during heating regeneration of the carbonaceous adsorbent may be supplied to the inlet of the desulfurization reactor, or it may be possible to add SO ₂ from other sources. May be supplied. Further, the NH ₃ gas injection may be performed by injecting a predetermined amount of NH ₃ gas from the start of the injection, or by increasing the injection amount in stages.

The carbonaceous adsorbent used in the present invention is
It is not limited to activated coke, etc. obtained by heat treatment or steam activation of conventionally used activated carbon and coal, etc., but refers to solid adsorbents containing free carbon, and metal oxidation agents such as vanadium. It may also contain something.

Note that the highly concentrated SOx gas recovered during regeneration is treated in a sulfuric acid, gypsum, or sulfur recovery process.

Hereinafter, the effects of the present invention will be clarified through experimental examples.

Example 1 After adding pitch and water to pulverized coal and kneading it, the diameter is about 4 mm.
970 ppm of SO ₂ was placed in a cross-flow moving bed reactor filled with the adsorbent obtained by press-molding it into a 5 mm column and carbonizing it with combustion exhaust gas at a temperature of 850 °C.
Coal-fired oiler exhaust gas containing 280 ppm NOx, 7.8% H ₂ O and 5.0% O ₂ was passed through at a temperature of 145°C. In this case, the space velocity of the gas was set to 600 hr ^-1 and the residence time of the adsorbent in the reactor was set to 48 hr. The desulfurization equipment is operated under the above conditions for up to 350 hours after the start of operation to repeat adsorption and regeneration, and then
The operation was carried out with 525 ppm of NH ₃ injected. Figure 2 shows the change in desulfurization rate in this case. As comparative examples, the results are also shown in FIG. 2 when NH ₃ was injected at 485 ppm from the beginning of operation (Comparative Example 1) and when NH ₃ was not injected throughout the period (Comparative Example 2).

Example 2 Same as Example 1, SO ₂ 150ppm, NOx 250ppm,
Steelworks sintering exhaust gas containing 9.5% H ₂ O and 14% O ₂ was passed through at 130°C. The space velocity in this case is
800 hr ⁻¹ and the residence time of the adsorbent in the reactor was set to 70 hours. The desulfurizer is operated under the above conditions for up to 700 hours from the start of operation, repeating adsorption and regeneration.
After that, 300 ppm of NH ₃ was injected into the exhaust gas and operation was carried out. The desulfurization rate and denitrification rate in this case are shown in Figure 3. As a comparative example, NH ₃ was
The results when 300ppm was injected (Comparative Example 3) were also the same.
Shown in the figure.

As described above, according to the present invention, at the beginning of operation of the desulfurization equipment, the exhaust gas is desulfurized without adding ammonia gas to the exhaust gas, and the adsorbent is repeatedly used to activate the adsorbent. Since ammonia gas is added to the untreated exhaust gas after this process, the desulfurization rate can be increased with high efficiency from the beginning of the desulfurization equipment operation, and a constant desulfurization rate can be maintained for a long time. Another important feature of the present invention is that activation of the carbonaceous adsorbent as a denitrification catalyst is also promoted, as shown in FIG.

[Brief explanation of the drawing]

Fig. 1 is a diagram showing an example of the present invention, Fig. 2 is a graph showing the results of changes in desulfurization performance over time in Example 1 and Comparative Examples 1 and 2, and Fig. 3 is a graph showing the results of changes in desulfurization performance over time in Example 1 and Comparative Examples 1 and 2. 2 is a graph showing changes over time in desulfurization and denitrification rates in 1... Ammonia gas storage tank, 2... Orthogonal moving bed desulfurization reactor, 3... Dust collector, 4... Adsorbent regenerator.

Claims (1)

[Claims] 1 After adding ammonia gas to the exhaust gas containing sulfur oxides, it is guided to a desulfurization equipment and brought into contact with a carbonaceous adsorbent to remove the sulfur oxides in the exhaust gas, and the inactivated adsorbent is regenerated by heating and repeated. In the exhaust gas desulfurization method used, at the beginning of operation of the desulfurization equipment, the exhaust gas is desulfurized without adding ammonia gas to the exhaust gas, and the adsorbent is activated by repeated use. A method for desulfurizing exhaust gas, which comprises subsequently adding ammonia gas to the untreated exhaust gas.